• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.4
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• pp.103-109
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• 2008

Semi-spherical CVT(SS-CVT) is one of friction drives, which transmits power via the friction force between a spherical shaped variator and output disks. The variator varies the speed ratio of SS-CVT continuously as well as transmits input power into the output shaft. Therefore two friction forces are normally applied on the variator; one is the longitudinal friction force for power transmission and the other is the lateral for shifting. In order to investigate the dynamic behavior of SS-CVT, we introduced a numerical model of 2-dimensional friction force using a function of slip ratio and slip angle. And a dynamic model, which describes the shifting mechanism of SS-CVT, is developed through 3-dimensional vector analysis. Finally we presented numerical results of the shift characteristics focused on the transient behavior of the variator's slip ratio and slip angle. The numerical results also show the typical CVT shifting characteristics of SS-CVT and stable shifting behaviors of the variator.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1187-1194
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• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.87-90
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• 2006

The Earth's spherical harmonic model of the main field and of the secular variation, of the geomagnetic field gives the intensity and geomagnetic structure at any location around the earth, assuming an undistorted, steady state field that no external sources or localized earth anamalies. To consider the practical use of a ship's digital compass in earth's magnetic field, Earth's spherical harmonic model is searched for the related practical methods and procedures as a basic study in this work.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.251-257
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• 1998

Spherical space frame structure with triangular network pattern, which has the various characteristics for the mechanic property, a funtional property, an aesthetic property and so on, has often been used as one of the most efficient space structures. It is expected that this type will be used widely in large-span structural roofs. But because this structure is made of network by combination of line elements there me many nodes therefore, the structure behavior is very complicated and there can be an overall collapse of structure by buckling phenomenon if the external force reaches a limitation. This kind of buckling is due to geometric shape, network pattern, the number of layer and so on, of structure. Therefore spherical space frame with triangle network pattern have attracted many designers and researchers attention all over the world. The number of layer of space frame is divided in to the simgle, double, multi layer. That is important element which is considered deeply in the beginning of structural design. The buckling characteristics of single-layer model and double-layer model for the spherical space frame structure with triangular network pattern are evaluated and the buckling loads of these types are compared with investigation their structural efficiency in this study.

• Smart Structures and Systems
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• v.14 no.2
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• pp.71-83
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• 2014

The purpose of this paper is to investigate the flexible structure of parabolic shell using photostrictive actuators. The analysis is made to know its dynamic behavior and light-induced control forces for coupled parabolic shell. The effects of an actuator location as well as membrane and bending components under the control action have been analyzed considering the approximate spherical model. The parabolic membrane shell accuracy is being mathematically approximated and validated comparing the light induced control forces using approximate equivalent spherical shell model. The parabolic shell with kapton smart material and photostrictive actuators has been used to formulate the governing equation in the transverse direction. The Kirchhoff-Love assumptions are used to obtain the governing equation of shell with actuator. The mechanical membrane forces and bending moments for parabolic thin shell with actuator is used to analyze the dynamic effect. The results show that membrane control action is much more significant than bending control action. Photostrictive actuators oriented along circumferential direction (actuator-2) can give better control effect than actuators placed along longitudinal direction (actuator-1). The slight difference is observed between spherical and parabolic shell for a surface with focal length to the diameter ratio of 1.00 or more than unity. Space applications often have the shape of parabolical shells or shell of revolution, due to their required focusing, aiming, or reflecting performance. The present approach is focused that photostrictive actuators can effectively control the vibration of parabolical membrane shell. Also, the actuator's location plays an important role in defining the control force.

• Journal of the Korean earth science society
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• v.37 no.2
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• pp.107-116
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• 2016

Stability of the barotropic Rossby-Haurwitz wave is investigated using the numerical models on the global domain. The Rossby-Haurwitz wave under investigation is composed of the basic zonal flow of super-rotation and a finite amplitude spherical harmonic wave. The Rossby-Haurwitz wave is given as either steady or unsteady wave by adjusting the strength of the super-rotating zonal flow. Stability as well as the growth rate of the wave in the numerical simulation is determined by comparing the perturbation amplitude at two different time stages. Unstable modes of the Rossby-Haurwitz wave exhibited a horizontal structure composing of various zonal-wavenumber components. The vorticity perturbation for some modes showed a discontinuity around the area of weak flow, which was found robust regardless of the horizontal resolution of the model. Fourier finite element model was shown to generate the unstable mode in earlier stage of the time integration due to less accuracy compared to the spherical harmonic spectral model. Taking the overall accuracy of the models into consideration, the time by which the unstable mode begin to dominate over the spherical harmonic wave was estimated.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1357-1365
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• 2009

In this study, we enhance the numerical approach of Lee et al.$^{(1)}$ to spherical indentation technique for property evaluation of hyper-elastic rubber. We first determine the friction coefficient between rubber and indenter in a practical viewpoint. We perform finite element numerical simulations for deeper indentation depth. An optimal data acquisition spot is selected, which features sufficiently large strain energy density and negligible frictional effect. We then improve two normalized functions mapping an indentation load vs. deflection curve into a strain energy density vs. first invariant curve, the latter of which in turn gives the Yeoh-model constants. The enhanced spherical indentation approach produces the rubber material properties with an average error of less than 3%.

• Structural Engineering and Mechanics
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• v.53 no.4
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• pp.661-679
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• 2015

In this article, nonlinear finite element solutions of bending responses of functionally graded spherical panels are presented. The material properties of functionally graded material are graded in thickness direction according to a power-law distribution of volume fractions. A general nonlinear mathematical shallow shell model has been developed based on higher order shear deformation theory by taking the geometric nonlinearity in Green-Lagrange sense. The model is discretised using finite element steps and the governing equations are obtained through variational principle. The nonlinear responses are evaluated through a direct iterative method. The model is validated by comparing the responses with the available published literatures. The efficacy of present model has also been established by demonstrating a simulation based nonlinear model developed in ANSYS environment. The effects of power-law indices, support conditions and different geometrical parameters on bending behaviour of functionally graded shells are obtained and discussed in detail.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.279-284
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• 2000

The existing microplane models for concrete ust three-dimensional spherical microplanes even in the analyses for two-dimensional members. Also, they can not describe accurately the post-cracking behavior of reinforced concrete in tension-compression. In this study, a new microplane model that is appropriate for the analyses of reinforced concrete planar members was developed to complement these disadvantages of the existing models. The proposed microplane model uses disk microplanes instead of the existing spherical ones. This new model is effective in numerical analysis because it uses less number of microplanes and two-dimensional stresses. Also, in this microplane model a concept of strain boundary was introduced to describe compressive behavior of reinforced concrete in tension-compression.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.6
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• pp.731-738
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• 2010

Cavitation is described by formation and collapse of the bubbles in a liquid when the ambient pressure decreases. Formed bubbles grow and collapse by change of pressure, and when they collapse, shockwave by high pressure is generated. In general, bubble behavior can be described by Rayleigh-Plesset equation under adiabatic or isothermal condition and hence, phase shift by the pressure change in a bubble cannot be considered in the equation. In our study, a numerical model is developed from the mathematical model considering the phase shift from the previous study. In the developed numerical model, size of single spherical bubble is calculated by the change of mass calculated from the change of the ambient pressure in a liquid. The developed numerical model is verified by a case of liquid flow in a narrow channel.