• Tribology and Lubricants
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• 제22권2호
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• pp.79-86
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• 2006

As the gerotor set with ideal profile meshes too tight, the reduction in the size of the rotor is generally adopted for a smooth operation. In this paper, a method of the profile modification for providing clearances was proposed. The meshing properties of the gerotor were analyzed and the non-boundary section of the inner rotor was identified, which denoted that the adjacent chambers were in the same pressure state. Clearances were imposed on the non-boundary section of the inner rotor, and then the profile of that section was modified as a composite curve of arcs. The other sections of the inner rotor were also interpolated as arcs. Thus, the whole profile of the inner rotor was designed as a composite curve of arcs.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2001년도 학술발표회 논문집(II)
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• pp.1133-1138
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• 2001

The focus of this paper is on the numerical investigation of obliquely incident wane interactions with a system composed of full submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing. The fully submerged systems allow surface and bottom clearances to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of fille second kind) tat satisfy the Helmholz governing equation. Using this computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, clearances. spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters call, if it is properly tuned to the coming waves, have good performances ill reflecting the obliquely incident waves over a tilde range of wave frequency and headings.

• 대한치과의사협회지
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• 제48권4호
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• pp.256-262
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• 2010

bone grafting is indicated in the case of bony defects and is classified into autograft, allograft, and xenograft. Synthetic bone graft is contrasted with these three categories in that it has a different donor source. Autograft is most prominent as it is known as a gold standard of all grafting procedures. Its principles and practices are well established via accumulated informations and clinical experiences, which imposes no regulations or restrictions in its clinical use. On the other hand, other bone graft procedures are under tight control for the safety and effectiveness of each product. Food and Drug Administration of the United States has a system in which the information on the approvals and clearances of bone graft materials on their internet homepage. All the bone graft materials that are under the regulations of the United States are classified into the category of medical devices, which includes allogenic bone, xenogenic bone, and synthetic bone graft materials. Each bone graft material has its own indication and the FDA approvals and clearances of medical devices contain the item of "intended use" to specify the indications of each bone graft materials. US dentists, as users of the specific bone graft materials, are provided with adequate information on the approved materials they are to utilize. As an user of these materials, Korean dentists are less provided with the information on the bone graft materials they want to use. Medical providers of the bone graft materials have to be able to provide their users with the essential information such as the intended use of the regulatory approval. Dentists must also be active in gathering informations on the material of their interest, and the system must be built in which both of the medical providers and users of bone graft materials can be satisfied in providing and getting the information, respectively.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.149-153
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• 2008

Since magnesium alloy sheets have been employed in industrial field which requires the light weight and thin engineering components, most of researches have been focused on the formability of magnesium ahoy sheet. In warm press forming of magnesium alloy sheet, it is important to control the sheet temperature by heating the sheet in closed die. When forming a commercial AZ31 magnesium alloy sheets which are 0.5mm and 1.0mm thick, respectively, time arriving at target temperature and temperature variation in magnesium alloy sheet have been investigated. Sheet metals were mostly formed in simple shapes such as circular or rectangular. Few studies about forming of complex shapes were reported. Thus, the formability of magnesium alloy sheet for complex shapes is investigated. The process variable for a double sink shape deep drawing with circular and rectangular shape was investigated by varying temperature, velocities, and clearances. Accordingly, temperature, velocities, and clearances suitable for forming were suggested through investigating the thickness variation of the product.

• 한국생산제조학회지
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• 제22권1호
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• pp.29-35
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• 2013

The pitch reducer consists of several planetary gearsets, and they should have good load distribution over gear tooth flank and load sharing among the planets to improve the durability. This work investigates how bearing internal clearances influence both the load distribution over the gear tooth flank and the planet load sharing. A whole system model is developed to analyze a pitch reducer. The model includes non-linear mesh stiffness of gears, non-linear stiffness of bearings. The results indicate that the face load factor and mesh load factor decrease, and the fatigue life of output shaft bearings increase as bearing internal clearances of output shaft decrease. Therefore, the internal clearance of output shaft bearing must be considered when designing the pitch reducer for wind turbines.

• Journal of Mechanical Science and Technology
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• 제18권6호
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• pp.979-989
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• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• Journal of Mechanical Science and Technology
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• 제16권6호
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• pp.799-809
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• 2002

In order to utilize a parallel mechanism as a machine tool component, it is important to estimate the errors of its end-effector due to the uncertainties in parts. This study proposes an error analysis for a new parallel device, a cubic parallel mechanism. For the parallel device, we consider two kinds of errors. One is a static error due to link stiffness and the other is a dynamic error due to clearances in the parts. In this study, we propose a stiffness model for the cubic parallel mechanism under the assumption that the link stiffness is a linear function of the link length. Also, from the fact that the errors of u-joints and spherical joints are changed with the direction of force acting on the link, they are regarded as a part of link errors, and then the error model is derived using forward kinematics. Lastly, both the error models are integrated into the total error, which is analyzed with a test example that the platform moves along a circular path. This analysis can be used in predicting the accuracy of other parallel devices.

• 대한조선학회논문집
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• 제41권6호
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• pp.24-32
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• 2004

The effects of guide vanes and tip clearances on the characteristics nf axial flow fans are investigated both computationally and experimentally. Performance test of fans carried out in full scale shows considerable effects of tip clearance between rotor tip and duct on the characteristics of fans. The tested results are compared with the computation based on the finite volume method to solve the Navier-Stoke equations with $textsc{k}$-$\varepsilon$ turbulence model. The comparison shows good agreements between experimental and computational results. In addition, the effects of shape of guide vanes are numerically studied. The results show that increased volume of separated region around the guide vane reduces the recovery of tangential component of kinetic energy in the wake, resulting in loss of efficiency

• 한국전산유체공학회지
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• 제18권1호
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• pp.7-12
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• 2013

This paper presents a numerical investigation of the influences of various non-uniform tip clearances on the performance and flow field in a centrifugal compressor. Numerical simulations were conducted for three centrifugal compressor impellers in which the tip clearance height varied linearly from the leading edge to the trailing edge. The numerical result was compared with the experimental data for validation. Although the performance improved for low tip clearances, a smaller tip clearance at the trailing edge reduced the overall tip leakage flow more effectively than a smaller tip clearance at the leading edge. Therefore, a smaller tip clearance at the trailing edge lowered the mixing loss caused by interactions between the tip leakage flow and the main passage flow.

• 대한기계학회논문집B
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• 제22권3호
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• pp.336-345
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• 1998

The substantial loss behind axial flow rotor was generated by wake, various vortices in the hub region and the leakage vortex in the tip region. Particularly, the leakage vortex formed near blade tip was one of the main causes of the reduction of performance, the generation of noise and the aerodynamic vibration in rotor downstream. In this study, the three-dimensional flowfields in an axial flow rotor for various tip clearances were calculated, and the numerical results were compared with the experimental ones. The numerical technique was based on SIMPLE algorithm using standard k-.epsilon. model (WFM). Through calculations, the effects of the tip clearance on the overall performance of rotor and the loss distributions, and the increase in the displacement, momentum, and blade-force-deficit thickness of the casing wall boundary layer were investigated. The mass-averaged flow variables behind rotor agreed well with the experimental results. The presence of the tip leakage vortex behind rotor was described well. Although the loci of leakage vortex by calculation showed some differences compared with the experimental results, its behavior for various tip clearances was clarified by examining the loci of vortex center.