• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.110-120
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• 1996

The purpose of this study is to build up the control scheme that promptly controls the pressure in a hydraulic cylinder having small control volume, using a PCV(proportional control valve) and a digital computer. Object pressure control system has the character to be unstable easily, because the displacement-flow gain of the PCV is so large considering comparatively small volume of the hydraulic cylinder and the time delay of response of PCV is long. Considering the above-mentioned characteristics of the object pressure control system, in this study, a control system is designed with two degree of freedom scheme that is composed by adding a feed-forward control path to I-PD control system, and the reference model is used to decide control parameters. And through some experiments on FF-I-PD, the validity of this control method is confirmed.

• Steel and Composite Structures
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• v.24 no.3
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• pp.359-367
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• 2017

In this work, transient heat transfer analysis of functionally graded (FG) carbon nanotube reinforced nanocomposite (CNTRC) cylinders with various essential and natural boundary conditions is investigated by a mesh-free method. The cylinders are subjected to thermal flux, convection environments and constant temperature faces. The material properties of the nanocomposite are estimated by an extended micro mechanical model in volume fraction form. The distribution of carbon nanotube (CNT) has a linear variation along the radial direction of axisymmetric cylinder. In the mesh-free analysis, moving least squares shape functions are used for approximation of temperature field in the weak form of heat transform equation and the transformation method is used for the imposition of essential boundary conditions. Newmark method is applied for solution time depended problem. The effects of CNT distribution pattern and volume fraction, cylinder thickness and boundary conditions are investigated on the transient temperature field of the nanocomposite cylinders.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1266-1274
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• 2001

Heat transfer phenomena during melting process of the phase change material (ice) was studied by numerical analysis and experiments. In a horizontal ice storage tube, the natural convection caused an increase in melting rate. However, the reduction of the heating surface area caused a decrease in melting rate. Therefore, during the melting process of ice in a horizontal cylinder, the reduction of the heating surface area should be considered. Under the same heating wall and initial water temperature condition, the melting rate became higher for $V_s/V_tot/=0.545 \;than \;that\; for\; V_s/V_tot$/=1.00 due to the difference in the reduction of heating surface area. A modified melting model considering the equivalent thermal conductivity of liquid phase and volume reduction was proposed. The results of the model were compared with the measured values and found to be in good agreement.

• Journal of Ocean Engineering and Technology
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• v.20 no.5 s.72
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• pp.15-22
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• 2006

A finite-volume method using multi-block grid technique has been developed in order to investigate the flow field around multi-body. Here the matching grids are used at the interface between blocks and the boundary conditions are imposed there to exchange physical values across the interface. For the test problems, the laminar viscous flaw around one-and two-cylinder are simulated and the results are compared with experiments and other numerical results.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.88-91
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• 2008

A Hybrid-Genetic-Algorithm based 3D-PTV has been constructed by introducing the conventional GA-3D-PTV. The measurement system consists of two-high-definition-cameras(1k ${\times}$ 1k), a Nd-Yag laser and a host computer. The system has been used to measure the wake of a cylinder. The Reynolds number is 1120. The structures of the wake have been quantified in detail than the results obtained ever before.

• Tribology and Lubricants
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• v.23 no.5
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• pp.201-206
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• 2007

The bent-axis type piston pump which is driven by the piston rod works on the way that the piston rod drives the cylinder block, so the taper angle of the piston rod and the swivel angle between the cylinder block and the shaft are very important design factors. If the above factors cannot satisfy the conditions of optimum design, the friction loss between the cylinder bore and the piston increases, and the pump can even fail to work under conditions of severe friction and wear. Since the piston reciprocates in the cylinder bore with high velocity, and at the same time it rotates on its own axis and revolves on the center of the cylinder block, the decrease of the volume efficiency generated on account of the leakage between the cylinder bore and the piston. Therefore, to prevent this case, the piston ring is designed at the end of the piston, and the friction characteristics between the piston ring and the cylinder bore are in need of research due to its great influence on the performance of piston pump. Thus, in this paper, the elastic hydraulic oil's lubrication analyses of the film thickness, the pressure distribution, and the friction force, and so on, have been performed, and the lubrication characteristics between the piston ring and the cylinder bore are explored by the results of the numerical analysis, and it is contributed to realize the higher efficiency and the more advanced performance of the bent-axis type piston pump.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.4
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• pp.91-98
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• 2011

Minimizing the cylinder wear and the consumption rate of cylinder oil in a large two-stroke diesel engine is of great economic importance. A motor-driven cylinder lubricator for Sulzer RT-flex large two-stroke diesel engines developed by authors is in need of mounting a quill system to lubricate cylinder parts for smoother operation. In order to apply the common-rail lubricating system to the developed cylinder lubricator as the second research stage, the quill system with a progressively quantitative distributor is improved in the electronically controlled quill system with an accumulating distributor. In this study, the effects of lubricator motor speed, plunger stroke and cylinder back pressure on oil feed rate, maximum discharge and delivery pressures are experimentally investigated by using the electronically controlled quill system with an accumulating distributor in the developed cylinder lubricator. It is found that the oil feed rate of the electronically controlled quill system with an accumulating distributor is larger than that of the quill system with a progressively quantitative distributor because of the increase of delivery speed and volume by changing the location of accumulator in the same experimental condition.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.4
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• pp.429-438
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• 2017

Cranke-Nicolson scheme in native OpenFOAM source libraries was not able to provide 2nd order temporal accuracy of velocity and pressure since the volume flux of convective nonlinear terms was 1st accurate in time. In the present study the simplest way of getting the volume flux with 2nd order accuracy was proposed by using old fluxes. A possible numerical instability originated from an explicit estimation of volume fluxes could be handled by introducing a weighting factor which was determined by observing the ratio of the finally corrected volume flux to the intermediate volume flux at the previous step. The new calculation of volume fluxes was able to provide temporally accurate velocity and pressure with 2nd order. The improvement of temporal accuracy was validated by performing numerical simulations of 2D Taylor-Green vortex of which an exact solution was known and 2D vortex shedding from a circular cylinder.

• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.925-934
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• 2003

An experimental study is performed to investigate the characteristics of near wake flow behind a circular cylinder with serrated fins using a constant temperature anemometer and flow visualization. Various vortex shedding modes are observed. Fin height and pitch are closely related to the vortex shedding frequency after a certain transient Reynolds number. The through velocity across the fins decreases with increasing fin height and decreasing fin pitch. Vortex shedding is affected strongly by the velocity distribution just on top of the finned tube. The weaker gradient of velocity distribution is shown as increasing the freestream velocity and the fin height, while decreasing the fin pitch. The weaker velocity gradient delays the entrainment flow and weakens its strength. As a result of this phenomenon, vortex shedding is decreased. The effective diameter is defined as a virtual circular cylinder diameter taking into account the volume of fins, while the hydraulic diameter is proposed to cover the effect of friction by the fin surfaces. The Strouhal number based upon the effective diameters seems to correlate well with that of a circular cylinder without fins. After a certain transient Reynolds number, the trend of the Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter. The normalized velocity and turbulent intensity distributions with the hydraulic diameter exhibit the best correlation with the circular cylinder's data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.285-293
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• 1997

Numerical calculations has been performed for the flow and heat transfer to a circular cylinder from a hot circular impinging air jet. The characteristics of the flow and heat transfer are investigated and compared with the two-dimensional flow. The present study lays emphasis on the investigation on the flow and heat transfer of the three-dimensionality. The effects of the buoyancy force and the size of jet are also studied. The noticeable difference between the three and the two-dimensional cases is that there is axial flow of low temperature into the center-plane of the cylinder from the outside in the recirculation region. Local Nusselt number over the cylinder surface has higher value for the large jet as compared with that of the small jet since the energy loss of hot jet to the ambient air decreases with increase of the jet size. As buoyancy force increases the flow accelerates so that the period of cooling by the ambient air is reduced, which results in higher local Nusselt number over the surface.