• Structural Monitoring and Maintenance
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• v.1 no.3
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• pp.309-322
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• 2014

Detection of fatigue cracks at an early stage of their development is important in structural health monitoring. The breathing of cracks in a structure generates higher harmonic components of the exciting frequency in the frequency spectrum. Previously, the residual operational deflection shape (R-ODS) method was successfully applied to beams with a single crack. The method is based on the ODSs at the exciting frequency and its higher harmonic components which consider both amplitude and phase information of responses to map the deflection pattern of structures. Although the R-ODS method shows the location of a single crack clearly, its identification for the location of multiple cracks in a structure is not always obvious. Therefore, an improvement to the R-ODS method is presented here to make the identification process distinct for the beams with multiple cracks. Numerical and experimental examples are utilised to investigate the effectiveness of the improved method.

• Coupled systems mechanics
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• v.5 no.4
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• pp.329-340
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• 2016

The trigonal shape memory alloys (SMAs) have a great potential to be utilized as the applications with special purposes, such as actuators with high operation frequency. Most studies on the trigonal microstructures typically focus on the well-known classic herringbone pattern, but many other patterns are also possible, such as non-classic herringbone, toothbrush and checkerboard patterns. In the current work, a systematic procedure is developed to find all possible laminate twin microstructures by using geometrically linear compatibility theory. The procedure is verified by SEM images with the information of crystallographic axes of unitcells obtained by EBSD, showing good agreement. Many interesting trigonal R-phase patterns are found in the specimen. Then, their incompatibility are analyzed with nonlinear compatibility theory. The relationship between such incompatibility and the likelihood of occurrence of the microstructures is revealed. The current procedure is rapid, computationally efficient and sufficiently general to allow further extension to other crystal systems and materials.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.2
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• pp.217-222
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• 1997

A simple finite element approach to predicting deformed shape and load-deflection curve of elastomers is presented in this paper. The method is based on several simplifications in deformation pattern and material behavior. The conventional updated Lagrangian approach is employed together with material data obtained by a simple tension test. The presented approach is verified through comparison of predicted results with experimental ones and applied successfully to shape design of various elastomers for shock, vibration and noise control. The advantage of the presented approach lies in easiness, simplicity and accuracy enough for engineering application.

• The Transactions of the Korea Information Processing Society
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• v.7 no.5
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• pp.1579-1586
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• 2000

This paper propose a method of shape analysis and representation for the handwritten Hangul character patterns. Each of the connected components composing a Hangul character is decomposed into many parts, and skeletons are extracted from the decomposed parts. Using the results, we represent the shape of Hangul characters using the attributed graph representation. A node of the attributed graph represents a part and an edge represents their relationships and they store valuable informations of the pattern shapes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.491-492
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• 2006

In the microstereolithography which can make 3-D microstructures, curing depth is different according to exposure energy. Curing depth has to be controlled to fabricate complex 3-D microstructures with overhang shape. It becomes increases when the exposure energy increases. And photocurable resin is cured when the exposure energy is bigger than critical energy. So optimal exposure energy has to be found to fabricate overhang structures without being gel. To make thinner layer, UV absorber is used and exposure pattern is changed. In this paper, we find curing characteristics according to exposure energy, and fabricate microstructures with overhang shape.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.2
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• pp.11-18
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• 2001

To clarify the influence of SAC shape of hole-type diesel nozzle on injection characteristics and spray patterns, the injection rate of three nozzle types(standard SAC nozzle, Needle-cut VCO nozzle and VCO nozzle) were measured by Zeuch's method and pictures of the sprays were taken by CCD camera. As the pump speed became higher, the injection characteristics of the three nozzles were different. Injection rate and perssure curves at the high pressure pipe in Needle-cut VCO nozzle were much more similar to the VCO nozzle than those of the SAC nozzle. When the needle was at pre-lift period for all speeds, the spray of the Needle-cut VCO nozzle showed almost the same shape as the SAC type nozzle. There was no differense in spray pattern at the needle full-lift periods.

• Journal of Korean Association for Spatial Structures
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• v.18 no.2
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• pp.25-34
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• 2018

This study investigated a bio-tensegrity structural system that combines the characteristics of a general tensegrity structural system with a biological system. The final research objective is to accomplish a changeability for the structural system as like the movement of the natural bio-system. In the study, we present a shape finding procedure for the two stage bio-tensegrity system model inspired by the movement pattern of animal backbone. The proposed system is allowing a dynamic movement by introducing the concept of "saddle" for the variable bio-tensegrity structure. Several shape finding analysis example and results are presented and shows a efficient validation and suitability.

• Current Optics and Photonics
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• v.2 no.4
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• pp.332-339
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• 2018

A new multi-frequency fringe projection method is proposed to reduce the nonlinear phase error in 3-D shape measurements using an adaptive compensation method. The phase error of the traditional fringe projection technique originates from various sources such as lens distortion, the nonlinear imaging system and a nonsinusoidal fringe pattern that can be very difficult to model. Inherent possibility of phase error appearing hinders one from accurate 3-D reconstruction. In this work, an adaptive compensation algorithm is introduced to reduce adaptively the phase error resulting from the fringe projection profilometry. Three different frequencies are used for generating the gratings of projector and conveyed to the four-step phase-shifting procedure to measure the objects of very discontinuous surfaces. The 3-D shape results show that this proposed technique succeeds in reconstructing the 3-D shape of any type of objects.

• Journal of the Korean GEO-environmental Society
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• v.14 no.9
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• pp.39-47
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• 2013

Local deformations in back filling materials of two sands and one glass bead with different particle shapes behind a rigid retaining wall were studied. Two kinds of boundary conditions were compared: active wall translation and active rotation of the wall about its toe. Effect of the speed of active wall translation was also investigated. The digital image correlation method was used to analyze local deformation developments inside the materials. Test results showed that particle shape and density mainly influence the inclination angle and width of the shear band. The general shear band pattern is strongly dependent on the wall movement mode, while it was little influenced by particle shape. Within a limited range of wall speed in this study, shear band became wider and local deformation became larger with increase of wall speed.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.392-397
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• 2001

This paper concerns on modal analysis of mechanical structures by using a continuous scanning laser Doppler vibrometer. In modal analysis the Hilbert transform based approach is superior to the Fourier transform based approach because of its fine accuracy and its flexible experimental settings. In this paper the Hilbert transform based approach is extended to measure area mode shape data of a structure by simply modifying the scanning pattern ranging the entire surface of the structure. The effectiveness of this proposed method is illustrated along with results of numerical simulation for a rectangular plate.