• Journal of the Korean Society for Precision Engineering
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• v.22 no.2
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• pp.79-88
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• 2005

Evaluating the effective properties of materials containing various types of in-homogeneities is an important issue in the analysis of structures composed of those materials. A simple and effective method for the purpose is to impose the periodic displacement boundary conditions on the finite element model of a unit cell. Their theoretical background is explained based on the purely kinematical relations in the regularly spaced in-homogeneity problems, and the strategies to implement them into the analysis and to evaluate the homogenized material constants are introduced. The creep behavior of a thin sheet with square arrayed rectangular voids is characterized, where the orthotropy is induced by the presence of the voids. The homogenization method is validated through the comparison of the analysis of detailed model with that of the simplified one with the effective parameters.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.944-949
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• 2003

This paper addresses the control of free and dynamic response of composite rotating pretwisted blade modeled as non-uniform thin-walled beam fixed at the certain presetting and pretwisted angle and incorporating piezoelectric induced damping capabilities. A distributed piezoelectric actuator pair is used to suppress the vibrations caused by external disturbances. The blade model incorporates non-uniform features such as transverse shear, secondary warping and includes the centrifugal and Coriolis force field. A velocity feedback control law relating the piezoelectiriccally induced transversal bending moment at the beam tip with the appropriately selected kinematical response quantity is used and the beneficial effects upon the closed loop eigenvibration and dynamic characteristics of the blade are highlighted.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.1059-1061
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• 2002

A FE model is to develop a personalized biomechanical model of the scoliotic spine that will allow the design of clinical test providing optimal estimation of the post-operation results. A flexible multi-body model of the spine including rib cage, clavicle, and scapular was developed to simulate several mobility simulations. Vertebrae, clavicle and scapular were represented using rigid bodies and ribs and sternum were modeled as flexible bodies. Kinematical Joints and spring elements were used to represent the intervertebral disc and ligaments respectively. Postero-anterior and lateral radiographics of a scoliotic spine were used to represent a 3D reconstruction. CT data for same patient were also used to verify vertebrae rotation driven from postero-anterior and lateral radiographic images. Simulated results showed good reducibility almost uniformly distributed along the spinal segments. It was also found that boundary and loading conditions, required to mimic the operation procedures, were proven to be very sensitive parameters to its results rather than its mechanical properties

• Journal of Biosystems Engineering
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• v.27 no.6
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• pp.513-520
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• 2002

A 5-row walking garlic harvester with pulling mechanism was developed in the study, based upon a kinematical analysis and related preliminary field tests on the conventional garlic harvesting method. The harvesting efficiency of the developed harvester was more than 98% in the garlic field irrigated before harvesting, 80-85% in the field without irrigation. The harvesting performance of the harvester was 660∼825㎡/hr at the forward speed of harvester of 0.3m/s in the irrigated field before garlic harvesting. For proper garlic drying and collection, the harvester discharged the harvested garlic on the ground uniformly at the angles of 135。∼150。 to its forward direction with the garlic bulb's placing toward the harvester. In the field tests, it was recommended that the forward speed of the harvester be approximately less than 0.2m/s, and that the spacing of planting garlic seeds should be standardized in the future fur increasing its harvesting efficiency.

• Fibers and Polymers
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• v.6 no.2
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• pp.151-155
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• 2005

A twisting machine is to twist yarns for improving yam strength. After twisting yams, the twisting machine winds yams into a bobbin. The traverse mechanism is very important part of winding mechanism. Because it performs uniform winding onto the bobbin. the traverse cam is the main part of the traverse mechanism. This paper proposes design method of the traverse cam using the relative velocity method [4,5]. The relative velocity method is used to calculate the relative velocity of the follower versus the cam at the center of roller, and then to determine the contact point using the geometric relationship and kinematical constraints. Finally, we present examples verifying the accuracy of the proposed methods.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.58.1-58.1
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• 2011

We present our N-body simulation study on the disk galaxy warp formation via close encounters. Using a publicly available code Gadget2, we investigate morphological and kinematical structures of disk galaxies while the galaxies are undergoing fly-by encounters with adjacent dark matter halos. In this study, we find that warps can be excited by impulsive encounters and sustained for a few billion years. Most of the warps from the simulation show inclination angles that are comparable to the observations. The creation of warps, their inclination and their lifetimes are governed primarily by the following three parameters: the impact parameter (the minimum distance between two halos), the mass ratio between two galaxies, and the incoming angle of the intruder. We discuss pros and cons about our alternative scenario in comparison with existing explanations.

• Structural Engineering and Mechanics
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• v.3 no.5
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• pp.411-427
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• 1995

The most known continuum damage theories for brittle structures are suitable to model the degradation of the material due to the deformation process and the consequent initiation of a macro-crack. Nevertheless, they are not able to describe the propagation of the crack that leads, eventually, to the breakage of the structure into parts that undergo rigid body motion. This paper presents a theory, formulated from formal arguments of Continuum Mechanics, that may describe not only the degradation but also the fracture of elastic structures. The modeling of such a discontinuous phenomenon through a continuous theory is possible by taking a cohesion variable, related with the links between material points, as an additional degree of kinematical freedom. The possibilities of the proposed theory are discussed through examples.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.442-449
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• 1999

Due to temperature variations, considerable longitudinal rail forces and displacements may develop in continuous welded rail(CWR) track on long-span bridges or viaducts. Excessive relative displacements between sleepers and ballast bed may disturb the stable position of the track in the ballast which results in a lower frictional resistance. Generally, these problems are solved by installing rail expansion devices. However the application of expansion devices in high-speed tracks on existing bridges, as a means to prevent excessive longitudinal displacements and forces, is not attractive method due to comfort, safety and maintenance aspects. An alternative and very effective solution is possibly the use of so-called zero longitudinal restraint(ZLR) fastenings over some length of the track. The calculations, carried out in this respect, show a considerable reduction of track displacements, track forces, and the relative sleeper/ballast displacements. This reduction depends on the length over which these fastenings are installed. In this paper calculations of the longitudinal displacments and forces in a CWR track and substructure resulting from thermal, mechanical and kinematical loads were carried out using the FEM analysis program LUSAS

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.2
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• pp.168-172
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• 2001

The accuracy problem of robot manipulators has long been one of the principal concerns in robot design and control. A practical and economical way of enhancing the manipulator accuracy, without affecting its hardware, is kinematic calibration. In this paper an effective and practical method is presented for kinematic calibration of Stewart platforms. In our method differential errors in kinematical parameters are linearly related to differential errors in the platform pose, expressed through the forward kinematics. The algorithm is tested using simulated measurement in which measurement noise is included.

• Structural Engineering and Mechanics
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• v.4 no.6
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• pp.613-630
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• 1996

The homogenization method is used to develop a beam element in space for thermo-mechanical analysis of unidirectional composites. Local stress and temperature field in the microscale are described using the function of homogenization. The global (macroscopic) behaviour of the structure is supposed to be that of a beam. Beam-type kinematical hypotheses (including independent shear rotations) are hence applied and superposed on the microdescription. A macroscopic stiffness matrix for such a beam element is then developed which contains the microscale properties of the single cell of periodicity. The presented model enables us to analyse without too much computational effort complicated composite structures such as e.g. toroidal coils of a fusion reactor. We need only a FE mesh sufficiently fine for a correct description of the local geometry of a single cell and a few of the newly developed elements for the description of the global behaviour. An unsmearing procedure gives the stress and temperature field in the different materials of a single cell.