• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.142-148
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• 2006

Hydraulic excavators have been popular devices in construction fields because of their multi-workings and economic efficiency. The mathematical models of excavators have many nonlinearities because of opening characteristics and dead zone of main control valve(MCV), oil temperature variation, etc. The objective of this paper is to develop a simulator for hydraulic excavator using AMESim. Components and their circuits are expressed graphically. Also, parameters and nonlinear characteristics are considered in a text style. From the simulation results, fixed spring stiffness of MCV can not obtain the satisfactory accuracy of spool displacement under whole P-Q diagrams. Closed loop type MCV containing a proportional gain, is proposed in this paper that can reduce displacement error. The ability of closed loop MCV is verified through comparing with normal type MCV using AMESim simulator. The excavator simulator can be used to forecast the attachment behaviors when components, mechanical attachments and hydraulic circuits change, or other control algorithms are applied. The simulator could be a kind of development platform for new excavators.

• Tribology and Lubricants
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• v.10 no.4
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• pp.82-88
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• 1994

This paper deals with a FEM computation as well as measurement of the contact force and distribution of the temperature in rubber lip seals when the sealing interference between the rotating shaft and the lip edge is present. The study of the contact forces and distributions of the temperature and the sealing contact stress has always been one of the basic steps in the process of designing a lip seal. The calculated FEM results indicate that as the sealing interference increases, the contact force moderately increases compared with decreased sealing interference at the seal lip edge and radically increases the contacting width. And the FEM computation of oontact forces including nonlinear problems has been compared with experimental measurements with good agreement. The frictional heat does not dissipate promptly in the rubber seal lip and tends to accumulate at the contacting lip edge especially.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.228-230
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• 1997

Recently, as power systems become large and complicated, chaos theory has been introduced to analyze their nonlinear characteristics. In this paper, voltage collapse phenomenon is more accurately analyzed using bifurcation theory of chaos. Chaotic behaviors has been observed in computer simulation for a simple power system over a range of loading conditions. Besides existence of voltage collapse point in critical value, operation of power system in Hopf window can be the cause of voltage collapse.

• Proceeding of KASS Symposium
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• 2005.05a
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• pp.167-172
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• 2005

In the dynamic analysis of cable structures, geometrical non-linearity due to the flexibility of cables must be considered efficiently. In this paper, formulation of tangent stiffness matrix of elastic catenary cable is derived by using relative nodal displacements, self-weight and unstressed cable length. Free vibration analysis of simply supported cable using elastic catenary cable elements is conducted and compared with that using truss elements. The result shows that elastic catenary cable elements are more compatible than truss elements in the case of analysis of cable structures. Furthermore, the characteristic of dynamic behaviors of cable structures by temporary unstability phenomenon is confirmed.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.493-498
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• 2003

The 3D nonlinear analysis for steel-concrete hybrid deck is carried out by utilizing 2D plane interface element. The effect of the slip occurred between steel and concrete can be modeled by this element. This analysis focuses on not only global behavior of steel-concrete hybrid deck but also local behaviors of members of it such as lower steel plate, I-beam, and concrete which are varied by slip modulus. In this analysis, it was founded that the limit slip modulus could classify the states of steel-concrete hybrid deck into three parts such as full-composite, partial-composite, and non-composite, considering the behavior of lower steel plate, I-beam, and concrete at the mid span and the support as well as the yield load and ultimate load of it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.906-910
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• 2003

This paper numerically analyzes the dynamic characteristics of a spindle system supported by two identical journal bearings considering bearing span that has dynamic load due to its mass unbalance. The Reynolds equation is transformed to solve a herringbone grooved journal bearing. The Reynolds equations are solved using FEM in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or angular displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the same bearing spans of upper and lower journal bearings produce the minimum runout and friction torque of a spindle system.

• Research in Mathematical Education
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• v.5 no.1
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• pp.1-12
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• 2001

Generating fractal images by graphing calculators such as TI_92 combines several important features, which convey the excitement of a living, changing mathematics appropriate to secondary or post-secondary students. The topic of fractal geometry can be illustrated using natural objects such as snowflakes, leaves and ferns. These complex and natural forms are often striking fantastic and beautiful. The examples highlight the fact that complex, natural behaviors can result from simple mathematical rules such as those embodied in iterated function systems(IFS). The visual splendor beauty of fractals, in concert with their ubiquity in nature, revels the intellectual beauty of nonlinear mathematics in a compelling way. The window is now open for students to experience and explore some of the wonder of fractal geometry.

• KSTLE International Journal
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• v.1 no.1
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• pp.43-47
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• 2000

Oil seals will experience a small amplitude dynamic excitation due to the shaft eccentricity as well as out-of-roundness of the shaft. The direct integration method is selected to analyze the time domain response of the seal lip-shaft contact. The physical properties of rubber seal materials are experimentally analyzed. Effects of both frequency and temperature on the material stiffness behavior are investigated for the linear viscoelastic materials of the seal. Using the nonlinear transient model, a finite element analysis of the lip-shaft contact behaviors under dynamic conditions is presented as a function of the shaft eccentricity, the shaft interference and the garter spring stiffness. The FEM results based on the experimental data indicate that the increased rotating speed may produce the separation conditions. These results will be very useful in predicting the leakage of oil seals under dynamic conditions.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.260-265
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• 2007

Rubber compounds have high viscoelastic property. One of the viscoelastic behaviors during profile extrusion is the swelling of extrudate. In this study, die swells of rubber compounds at the capillary die have been investigated through experiment and computer simulation. Experiments and simulations have been performed using fluidity tester and commercial CFD code, Polyflow respectively. Die swells of rubber compounds in a capillary die were predicted using non-linear differential viscoelastic model, Phan-Thien-Tanner(PTT) model for various relaxation times and relaxation modes. The results of simulation were compared with the experiments. Pressure and velocity distribution, and circulation flows at the comer of capillary die have been investigated through computer simulation. It is concluded that the PTT model successfully represented the amount of the die swell of rubber compounds for various relaxation times at different modes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.260-265
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• 1997

Large dynamic loads act on the rotor in rotary compressors. There are unbalance forces due to eccentric rotation parts and gas forces induced by the difference in pressure between compression and suction gases6 Rotor-journal bearing system is nonlinear since the stiffness and damping coefficients of the lubricating oil film are not constant in the bearings. In this paper, the program for predicting the behaviors of rotor-journal bearing system of rotary compressor is developed. Finite element modeling is used to analyze the flexible rotor. The numerical results are compared with experimental results. The location of balancer weight are suggested for reducing rotor whiring displacement.