• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1828-1831
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• 2003

There are various sources causing a position error in a linear motor. This paper focuses on error sources from rotational motions of a table and friction. Rotational errors occur due to imperfections during manufacturing and/or assembly of guide ways, and cause a position error at locations of interest. Friction is another factor deteriorating the position error due to its highly nonlinear behavior. The position error of the linear motor was about 20∼30$\mu\textrm{m}$. After compensating the position errors due to rotational error motions and friction. the remaining errors become about 6～8$\mu\textrm{m}$ and 2～3$\mu\textrm{m}$, respectively. It is shown that the positional accuracy of a linear can be greatly improved by compensating the two error sources.

• Steel and Composite Structures
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• 제5권1호
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• pp.1-15
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• 2005

Important characteristics of the previously proposed reduced stiffness method and a summery of its design curves for the buckling of the axially loaded sandwich cylindrical shells is presented. Comparison of the lower bound obtained with FEM analysis with that from the reduced stiffness analysis shows that the proposed reduced stiffness method can provide safe lower bounds for the buckling of geometrically imperfect, axially loaded sandwich cylindrical shells. One of the attractive features of the reduced stiffness elastic lower bound analysis is that it provides safe estimates of buckling loads that do not depend on the specification of the precise magnitude of the imperfection spectra. As a result, designers can readily apply this method without being worried about possible geometrical imperfections that might be generated during fabrication and construction of sandwich cylindrical shells.

• Computers and Concrete
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• 제1권4호
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• pp.433-455
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• 2004

The paper presents results of FE-calculations on shear localizations in quasi-brittle materials during both an uniaxial plane strain compression and uniaxial plane strain extension. An elasto-plastic model with a linear Drucker-Prager type criterion using isotropic hardening and softening and non-associated flow rule was used. A non-local extension was applied in a softening regime to capture realistically shear localization and to obtain a well-posed boundary value problem. A characteristic length was incorporated via a weighting function. Attention was focused on the effect of mesh size, mesh alignment, non-local parameter and imperfections on the thickness and inclination of shear localization. Different methods to calculate plastic strain rates were carefully discussed.

• Wind and Structures
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• 제12권2호
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• pp.89-101
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• 2009

The Monte Carlo procedure was used to simulate wind load effects on a light-frame low-rise structure of irregular shape and a main wind force resisting system. Two analytical models were studied: rigid-beam and rigid-plate models. The models assumed that roof diaphragms were rigid beam or rigid plate and shear walls controlled system behavior and failure. The parameters defining wall stiffness, including imperfections, were random and included wall stiffness, wall capacity and yield displacements. The effect of openings was included in the simulation via a set of discrete multipliers with uniform distribution. One and two-story buildings were analyzed and the models can be expanded into multiple-floor structures provided that the assumptions made in this paper are not violated.

• Steel and Composite Structures
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• 제24권5호
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• pp.591-602
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• 2017

A cable-stiffened cylindrical single-layer latticed shell that is reinforced by cable-stiffened system has superior stability behaviour compared with the ordinary cylindrical latticed shell. The layouts of cable-stiffened system are flexible in this structural system, and different layouts contribute different stiffness to the structure. However, the existed few research primarily focused on the simplest type of cable layouts, in which the grids of the latticed shell are diagonally stiffened by prestressed cables in-plane. This current work examines the stability behaviour of the cable-stiffened cylindrical latticed shells with two different types of cable layouts using nonlinear finite element analysis. A parametric study on the effect of cross-sectional of the cables, pretension in cables, joint stiffness, initial imperfections, load distributions and boundary conditions is presented. The findings are useful for the reference of the designer in using this type of structural system.

• Smart Structures and Systems
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• 제25권5호
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• pp.619-630
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• 2020

This paper studies nonlinear free vibration characteristics of nonlocal magneto-electro-elastic (MEE) nanobeams resting on nonlinear elastic substrate having geometrical imperfection by considering piezoelectric reinforcement scheme. The piezoelectric reinforcement can cause an enhanced vibration behavior of smart nanobeams under magnetic field. All of previously reported studies on MEE nanobeams ignore the influences of geometric imperfections which are very substantial due to the reason that a nanobeam cannot be always perfect. Nonlinear governing equations of a smart nanobeam are derived based on classical beam theory and an analytical trend is provided to obtained nonlinear vibration frequency. This research shows that changing the volume fraction of piezoelectric constituent in the material has a great influence on vibration behavior of smart nanobeam under electric and magnetic fields. Also, it can be seen that nonlinear vibration behaviors of smart nanobeam are dependent on the magnitude of exerted electric voltage, magnetic potential, hardening elastic foundation and geometrical imperfection.

• 제어로봇시스템학회논문지
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• 제8권6호
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• pp.498-505
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• 2002

Reducing odometer errors caused by kinematic imperfections in wheeled mobile robots is imestigated. Wheel diameters and wheelbase are corrected by using encoders without landmarks. A new velocity trajectory is proposed that compensates for an orientation error due to acceleration- resolution constraints on motor controllers. Based on this velocity trajectory, the wheel velocity of one out of two driven wheels may be changed by the traveled distance of the mobile robot. It is shown that a wheeled mobile robot can't move along a straight line exactly, even if kinematic correction are achieved perfectly, and this phenomenon is attributable to acceleration-resolution constraints on motor controllers. We experiment on a wheeled mobile robot with 2 d.o.f. are used in the experiment to verify the proposed scheme.

• ETRI Journal
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• 제23권2호
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• pp.85-95
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• 2001

The surface modeling capability of CAD systems is widely used to design products bounded by free form surfaces and curves. However, the surfaces or curves generated by popular data fitting methods usually have shape imperfections such as wiggles. Thus, fairing operations are required to remove the wiggles, which makes the surfaces or curves smooth. This paper proposes a new method based on the wavelet transform for fairing the surfaces or curves while preserving the continuity with adjacent surfaces or curves. The wavelet transform gives a hierarchical perspective of the surfaces and the curves, which can be decomposed into the overall sweep and details, i.e., local deviations from sweep like the wiggles. The proposed fairing method provides a similar effect on the mathematical surface as that of the grinding operation using sandpaper on the physical surface.

• 한국해양공학회지
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• 제16권1호
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• pp.46-51
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• 2002

Fatigue life estimation by the theoretical stress concentration factors are, in general, considerably different from test results. And in calculating stress concentration factor, it is very difficult to consider actual geometry and material property which are the notch shapes, imperfections or defects of materials such as porosities inclusions and casting defects, etc. Therefore, the paper deals with the experimental method to find out the more exact stress concentration factors by measuring the strain distributions on each specimen by 3D-ESPI(Electronic Speckle Pattern Interferometry) System. Then the fatigue lives are compared between theoretical calculations using stress concentration factors determined by 3D-ESPI system and fatigue test results.

• 한국해양공학회지
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• 제10권4호
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• pp.28-37
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• 1996

A finite element analysis code considering elasto-plastic large deformation is developed to predict the ultimate strength of circular cylinders subject to external pressure loading by introducing a new type of axisymmetric shell element which can take into account the plasticity effect due to the circumferential bending while drastically saving the computing efforts compared with the tree dimensional finite element analysis. It is observed that analsis results of present approach show good agreement with the test results of previous works. Parametric study gives the effects of initial imperfections on ultimate strength ahd this information is recommended to be used to modify the actual test data to the ones which can be used more reasonably in making empirical design formulas.