• Tribology and Lubricants
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• 제11권1호
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• pp.5-11
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• 1995

This paper addresses the lubrication analysis of a short squeeze film damper operating with electro-rheological (ER) fluids which have large and reversible changes in yield shear stresses with respect to an applied electric field. The ER fluids are assumed to be modeled as Bingham fluids. The governing lubrication equation for the ER short squeeze film damper is developed on the basis of a Bingham fluid model, and the equation is subsequently solved in order to investigate the effects of the ER fluids on the damping capability of the damper. It is shown that a substantial increase in damping (both direct and cross coupled) is accomplished by increasing the yield shear stress of the ER fluids. This significant improvement of the damping capability suggests that the ER short squeeze film damper could be very effective for reducing the vibration and controlling the critical speeds of a rotor system.

• 유공압시스템학회:학술대회논문집
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• 유공압시스템학회 2010년도 춘계학술대회
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• pp.33-38
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• 2010

As for an oil hydraulic vane pump of vehicle hydraulic systems, the highest of planning technique required by the acquisition of optimum profile data which can be available to predict noises and vibrations. Pressure pulsation may result in considerable vibration and noise of pump component as well as cavitation in hydraulic system. The influences of the discharge pressure and rotating speed of the vane on the dynamic pressure in chamber surrounding a vane have been investigated. It is very important to predict pressure pulsation in vane pump. This paper presents analysis of technique of vane pump for automatic transmission. The predicted result using AMESim model were good agreement with the experimentally obtained results.

• 소음진동
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• 제10권1호
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• pp.97-106
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• 2000

The dynamic behavior of crankshaft-bearing system in scroll compressor has been investigated using the combined methodologies of finite elements and transfer matrices. The finite element formulation is proposed including the field element for a shaft section and the point element at balancer weight locations, bearing locations, etc., whereas the conventional method is used with the elements. The Houbolt method is used to consider the time march for the integration of the system equations. The linear stiffness and damping coefficients are calculated for a finite cylindrical fluid-film bearing by solving the Reynolds equation, using finite difference method. The orbital response of crankshaft supported on the linear bearing model is obtained, considering balancer weights of motor rotor. And, the steady state displacement of crankshaft are compared with a variation in balancer weight. The loci of crankshaft at bearing locations are composed of the synchronous whirl component and the non-synchronous whirl component.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.375-382
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• 2009

Hydraulic instability associated with pressure fluctuations is a serious problem in hydraulic machinery. Pressure fluctuations are usually a result of a strong vortex created in the centre of a flow at the outlet of a runner. At every radial turbine and also at every single regulating axial turbine, the draft tube vortex appears at part-load operating regimes. The consequences of the vortex developed in the draft tube are very unpleasant pressure pulsation, axial and radial forces and torque fluctuation as well as turbine structure vibration. The consequences of the vortex are transferred upstream and downstream with amplitude and frequency modulation in respect of the turbine operating regime, cavitation conditions and air admitted content. Numerical prediction of the vortex appearance in the design stage is a very important task. The amplitude of the pressure pulsation is different for each operating regime therefore the main goal of this research was to numerically predict pressure pulsation amplitude versus different guide vane openings and to compare the results with experimental ones. For the numerical flow analysis of a complete Francis turbine (FT), the computer code ANSYS-CFX11 has been used.

• 한국유체기계학회 논문집
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• 제12권4호
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• pp.14-22
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• 2009

The head-capacity curves for pumps developed by the pump manufacturer are based on tests of a single pump operating in a semi-infinite basin with no close walls or floors and with no stray currents. Therefore, flow into the pump intake is with no vortices or swirling. However, pump station designers relying on these curves to define the operating conditions for the pump selected sometimes meet the reductions of capacity and efficiency, as well as the increase of vibration and additional noise, which were caused by air-entered flow in the pump station. From this background, the authors are carrying out a systematic study on the flow characteristics of intakes within a sump of pump station model. Multi-intake sump model with anti-submerged vortex device basin is designed and the characteristics of submerged vortex is investigated in the flow field by numerical simulation. In this study, a commercial CFD code is used to predict the vortex generation in the pump station accurately. The analysed results by CFD show that the vortex structure and effect of anti-submerged vortex device are different at each pump intake channel.

• 항공우주시스템공학회지
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• 제9권3호
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• pp.1-7
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• 2015

In this study, the design of compound smart materials hydraulic pump that can be applied to a small-medium size UAV having a limited space envelope and weight has been conducted. Compound Smart Material Pump(CSMP) proposed in this paper is composed of a pressurize pump and a flow pump for supplying the high pressure and fluid displacement to overcome the disadvantages of the piezoelectric actuator which has a small strain. Though this compound smart material pump has been designed as small size and lightweight as possible, it can sequentially supply the sufficient large flow rate and pressure required for the brake operation. For the design of CSMP, about 2,700 kg (6,000 lb) class fixed wing manned aircraft was selected. Based on the established requirements, the design of the CSMP have been done by strength, vibration, and fluid flow analysis.

• Earthquakes and Structures
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• 제24권5호
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• pp.333-343
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• 2023

Various seismic isolation and reduction devices have been applied to suppress the longitudinal vibration of continuous girder bridges. As representative devices, lead rubber bearing (LRB) and fluid viscous damper (FVD) might suffer from deterioration during the long-term service. This study aims to evaluate the impact of device deterioration on the seismic responses of continuous girder bridges and investigate the seismic behavior of deteriorated LRBs and FVDs. Seismic performance of a simplified bridge model was investigated, and the influence of device deterioration was evaluated by the coefficient of variation method. The contribution of LRB and FVD was assessed by the Sobol global sensitivity analysis method. Finally, the seismic behaviors of deteriorated LRBs and FVDs were discussed. The result shows that (i) the girder-pier relative displacement is the most sensitive to the changes in the deterioration level, (ii) the deterioration of FVD has a greater effect on the structural responses than that of LRB, (iii) FVD plays a major role in energy dissipation with a low degradation level while LRB is more essential in dissipating energy when suffering from high degradation level, (iv) the deteriorated devices are more likely to reach the ultimate state and thus be damaged.

• 한국소음진동공학회논문집
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• 제26권2호
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• pp.165-171
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• 2016

A prosthetic knee for above-knee (AK) amputee is categorized into passive and active type. The passive prosthetic knee is generally made by elastic material. Although AK amputee can easily walk by using passive prosthetic leg, knee joint motions are not similar to ordinary persons. The active prosthetic leg can control the knee angle owing to the actuator and microprocessor. However, the active type is not cost-effective and the stability may be lost due to the malfunction of sensors. In order to resolve these disadvantages of passive and active type, a semi-active prosthetic knee which can control the knee angle is proposed in this work. The proposed semi-active one requires a less input energy but provides active type performance. In order to achieve this goal, in this work, a semi-active prosthetic knee using magneto-rheological (MR) damper for AK amputees is designed. The MR damper can support the weight of body by using less energy than actuator of active prosthetic. It can control knee angle by inducing the magnetic field at the time of stance phase. This salient characteristic is evaluated and presented in this work.

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.800-807
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• 2012

In this paper, radiation efficiency of the plate surround by an infinite rigid baffle is studied. The plate is simply supported and one side is in contact with air, while other side with water. The pressure and normal velocity over the plate surface are assumed as modal summations, from which a set of linear equations is obtained for fluid-structure coupled problem. It is shown that neglect of the cross modes results in overestimation of the radiation efficiency specifically for mid-frequency ranges. Based on the fact that the responses are mainly determined from the first few cross modes in addition to the diagonal terms, a new algorithm is proposed, where banded matrix is iteratively solved in computing radiation efficiency. In numerical examples, it is found that radiation efficiency obtained from banded matrix is in excellent agreement with the one from the full matrix, while computing time is significantly reduced. It is also found that as frequency grows larger, radiation efficiency considering only diagonal terms is a good approximation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.289-294
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• 2002

In this study, performance, flow characteristics and noise of a cross-flow-fan system, used in indoor unit of the split-type air conditioner, were predicted by computational simulation. Triangular elements were used to mesh the calculation domain and quadrilateral elements were attached to the blade surfaces and walls to enhance the simulation quality. The unsteady incompressible Wavier-Stokes equations were solved using a sliding mesh technique on the interface between rotating fan region and the outside. Two stripes of velocity stream inside the cross-flow-fan were shown - the one was due to the eccentric vortex and the other was due to the normal entrance flow. As the flow rate increased, the center of the eccentric vortex moved toward the inner blade tip and rear-guide, and the exiting flow still had velocity variation along the stabilizer, which can increase the noise level. The acoustic pressure was calculated by using Lowson's equation. From the calculated acoustic pressure, it was found that the trailing edge is a dominant of acoustic generation.