• Transactions of The Korea Fluid Power Systems Society
• /
• v.3 no.3
• /
• pp.1-7
• /
• 2006

In this paper, a theoretical analysis is carried out to study the lubrication characteristics of sealless piston for hydraulic cylinders. The analytical pressure distributions are obtained solving one-dimensional Reynolds equation with partially tapered moving piston. Nearly analytical expressions for lateral forces acting on the piston and leakage flow rate through the clearance are also presented. Using the analytical expressions, the influence of design parameters on lubrication characteristics can be easily evaluated without numerical analysis. Composite-shaped piston which minimizes the leakage flow rate is the optimum in sealless piston for hydraulic cylinder.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1991.10a
• /
• pp.75-80
• /
• 1991

The purpose of this study is to ascertain the robustness of p-version model with hierarchic intergrals of Legendre shape functions in various applications including plane stress/strain, axisymmetric and shell problems. The most important symptoms of accuracy failure in modern finite elements are spurious mechanisms and a phenomenon known as locking which are exhibited for incompressible materials and irregular shapes which contain aspect ratios(R/t, a/b), tapered ratio(d/b), and skewness. The condition numbers and energy norms are used to estimate numerical errors, convergence characteristics and algorithmic efficiencies for verifying the aforementioned symptoms of accuracy failure. Numerical results from p-version models are compared wi th those from NASTRAN, SAP90, and Cheung's hybrid elements.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.2
• /
• pp.189-197
• /
• 1996

In this study, the crashworthiness analysis was carried out for the hat type section side rails which had an important role of absorbing the impact energy during frontal crash. In case of a tapered hat type section model, numerical simulation models and test models were designed with varing design variables; welding pitch, taper angle, initiator shape, initiator location. The effect of variation of the design variables was investigated by quasi-static and dynamic test and numerical simulation.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.14 no.1
• /
• pp.87-93
• /
• 2001

이 논문은 사하중에 의한 정적 처짐을 갖는 변단면 보의 자유진동에 관한 연구이다. 사하중이 작용하는 변단면 보의 자유진동을 지배하는 상미분방정식을 유도하고 이를 수치해석하여 최 저차 3개 모드의 고유진동수 및 진동형을 산출하였다. 수치해석 예제에서는 선형 변단면과 등분포 사하중을 채택하였다. 지점조건으로는 회전-회전, 회전-고정, 고정-고정 보를 채택하였다. 수치해석의 결과로 하중강도, 세장비 및 단면비가 고유진동수에 미치는 영향을 분석하였다. 사하중의 영향을 고려한 경우와 고려하지 않은 경우의 진동형을 서로 비교하였다.

• Journal of the Korean Society for Precision Engineering
• /
• v.23 no.9 s.186
• /
• pp.127-133
• /
• 2006

Cold expansion method is used to protect a fatigue fracture from fastener hole in the structure and aerospace industry. Cold expansion is that an oversized tapered mandrel goes through the hole and produces a compressive residual stress as well as plastic deformation around the hole. Here, mandrel shapes are one of the factors which are influenced on the residual stress distribution by cold expansion method. This paper, according to mandrel shapes (diameter of mandrel, length of mandrel and length of taper), we are performed a finite element analysis of residual stress distribution by cold expansion method. From this study, it has been found that diameter of mandrel and length of taper are an important factor which was generated a low compressive residual stress surround of fastener hole by cold expansion method.

• Journal of the Korean Society for Precision Engineering
• /
• v.10 no.1
• /
• pp.114-125
• /
• 1993

Thermoelastoplastic analysis of a typical device consisting of fixed tube and movable case having an inital clearance in between, which is subjected to pressure and thermal load, has been carried out to examine the cause of malfunction mainly at high temperature condition, and to improve the design. Stresses, deformed shape, interface state and their effects on normal function of case are discussed by using finite element method. The extraction energy can be remarkably reduced by changing the configuration of tube from the present design (Parallel type) to the improved design (Tapered type). This effect has been proved by sustained cyclic function test.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1991.04a
• /
• pp.22-31
• /
• 1991

Machining with boring bars frequently induce chatter vibration because of the low stiffness and damping of cantilever shape of boring bars. To increase stiffness and damping, a carbon fiber epoxy composite boring bar was designed, manufactured and tested. The natural frequency of the carbon fiber epoxy composite boring bar in the free-free end condition was incerased more than 50% over that of the steel boring bar, and the damping of the carbon fiber epoxy composite boring bar was also increased 450%. The fundamental natural frequency of the carbon fiber epoxycomposite boring bar in the cantilever beam condition was found to be increased 20-30% over that of the steel boring bar in overhang length range 140-200mm. In machining S45C tapered workpieces, the limit of the overhang length of the steel boring bar was about 170mm in cutting speed 140m/min.

• Mycobiology
• /
• v.42 no.4
• /
• pp.317-321
• /
• 2014

Fruiting bodies similar to those of the ascomycete fungi Podostroma cornu-damae and Cordyceps militaris were collected from Mt. Seunghak in Busan, Korea on August 21, 2012. The fruiting bodies were cylindrical, with tapered ends and golden red in color. The fruiting bodies contained abundant conidiophores bearing single-celled conidia, but no perithecia or asci. Pure culture of the fungal isolates was obtained through single-spore isolation. Analyses of morphological characteristics, including conidia shape, and phylogenetic traits, using internal transcribed spacer sequences, showed that these isolates belonged to the species Simplicillium lanosoniveum. Although this fungal species is known to be mycoparasitic, the isolates obtained in this study were unable to infect fungi. However, silkworms (Bombyx mori) inoculated with the fungal isolates died during the larval or pupal stages, as has been shown for the strongly entomopathogenic fungus Beauveria bassiana. This study is the first report of the entomopathogenicity of S. lanosoniveum and indicates its potential for use in biological control of insects.

• Proceedings of the KSME Conference
• /
• 2001.06b
• /
• pp.590-595
• /
• 2001

To improve the modeling accuracy for the finite element method, this paper proposes a method to make a combined use of finite elements and exact dynamic elements. Exact interpolation functions for a Timoshenko beam element are derived and compared with interpolation functions of the finite element method (FEM). The exact interpolation functions are tested with the Laplace variable varied. The exact interpolation functions are used to gain more accurate mode shape functions for the finite element method. This paper also presents a combined use of finite elements and exact dynamic elements in design problems. A Timoshenko frame with tapered sections is tested to demonstrate the design procedure with the proposed method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.1000-1004
• /
• 2001

This study explores the free vibrations of tapered column with hinged end restricted by rotational spring. The ordinary differential equation governing the free vibration of such column is derived as nondimensional form in which three kinds of cross-sectional shape are considered. In order to obtain the natural frequencies of column, the governing differential equation is solved by numerical procedures. Numerical results are compared with existing solutions by other methods. It is expected that the results obtained herein can be practically utilized in the structural and the vibration control fields.