• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.155-161
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• 2000

It is very important to control the final load that acts on a support system, in tunnel engineering. A reliable analysis is needed to carry out technically reasonable design and safe construction. Also, a series of procedures of construction and the rock-support interaction behavior must be considered. Most existing studies have been performed as the limited analysis based on the simplified assumption. In this study, through the analysis of a circular tunnel using a 2-D finite differential code, the rook-support interaction behaviors in the variation of rock and stress conditions are analyzed and compared with the results from the closed form solutions. Consequently, more realistic rock-support interaction curves are obtained by including the effects of initial stresses and rock condition. These cures are very useful to predict the required support pressure in the initial design stage.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.403-409
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• 2000

It is very important to control the final load that acts on a support system, in tunnel engineering. A reliable analysis is needed to carry out technically reasonable design and safe construction. Also, a series of procedures of construction and the rock-support interaction behavior must be considered. Most existing studies have been performed as the limited analysis based on the simplified assumption. In this study, through the analysis of a circular tunnel using a 2-D finite differential code, the rock-support interaction behaviors in the variation of rock and stress conditions are analyzed and compared with the results from the closed form solutions. Consequently, more realistic rock-support interaction curves are obtained by including the effects of initial stresses and rock condition. These curves are very useful to predict the required support pressure in the initial design stage.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.1 s.343
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• pp.33-40
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• 2006

This paper presents a novel surface acoustic wave (SAW)-based pressure sensor, which is composed of single phase unidirectional transducer (SPUDT), three reflectors, and a deep etched substrate for bonding underneath the diaphragm. Using the coupling of modes (COM) theory, the SAW device was simulated, and the optimized design parameters were extracted. Finite Element Methods (FEM) was utilized to calculate the bending and stress/strain distribution on the diaphragm under a given pressure. Using extracted optimal design parameters, a 440 MHz reflective delay line on 41o YX LiNbO3 was developed. High S/N ratio, shan reflection peaks, and small spurious peaks were observed. The measured S11 results showed a good agreement with simulated results obtained from coupling-of-modes (COM) modeling and Finite Element Method (FEM) analysis.

• Composites Research
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• v.15 no.5
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• pp.7-13
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• 2002

The piezoelectric thin film sensor has good characteristics to observe the impact responses of composite structures. The capabilities for monitoring impact behavior of Gr/Ep laminates subjected to damage-induced impact using the PVDF(polyvinylidene fluoride) film sensor were examined. For a series of low-velocity impact tests from low energy to damage-induced energy, simulated sensor signals were compared with measured signals and the PVDF film sensor. Local impact damages(matrix cracking and delamination) were found at three impact tests, but the measured signals agreed well with the simulated sensor signals based on the linear relationship between the impact forces and the PVDF film sensor signals. And the inverse technique was applied to reconstruct the impact forces using the PVDF film sensor signals. Most of reconstructed impact forces had good agreement with the measured forces. The comparison results showed that the local damage due. to low-velocity impact didn't disturb the global impact responses of composite laminates and the reconstruction of impact forces from PVDF sensor signals wasn't affected by the local damage.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.381-386
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• 2014

In order to investigate the effect of contact load, which is one of the fretting corrosion factors affecting the electric connector, a coupled fretting corrosion specimens were prepared using a tin-plated brass coupon with a thickness of $3{\mu}m$. Electric resistance of the contact was measured during the fretting corrosion test period. There was increase in resistance with fretting cycles. The change in resistance can be classified by 3 stages. The first stage exhibited low and stable resistance. Second stage showed steady increment of the resistance and third stage showed very high and intermittent resistance. The relationship between the failure cycle (Nf) and contact force (P) can be drawn as; It is possible to draw the prediction equation for the failure cycle of the electric connector corresponding to the very high and intermittent resistance under various environment conditions through the fretting tests under various conditions such as load, displacement, temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1528-1534
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• 2001

In order to improve Leak-Be(ore-Break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result.

• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.267-277
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• 1999

The pushover analysis technique is now attracting the world-wide interest for the prediction of elastic and inelastic behavior of structures in the seismic evaluation of existing buildings. However, the reliability of this analysis technique has not been fully checked by the test results in the case of structures with nonseismic details. The objective of this study is to verify the correlation between the experimental and analytical responses of a 1:12 scale 10-story reinforced concrete frame with non-seismic details by using DRAIN-2DX program and the test results performed previously. It is concluded from this comparison that the overall responses such as the relations between story shear versus interstory drift and the local deformations such as plastic rotations can be predicted with quite high reliability.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.10
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• pp.10-20
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• 2003

In this study, the effective properties were numerically calculated for laminated plain weave textile composites with arbitrary s tacking orientation angles. A single-field macroelement with modified sub-domain integration was used in the analysis to reduce computer resource requirement while efficiently accounting for the internal microstructure. A sample calculation procedure based on the Monte Carlo method was employed to consider the random shift between the layers. Results showed that a significant deviation occurred when the orientation angles were near 0 deg for extensional modulus and Poisson's ratio and 45 deg for the shear modulus. It was also found that the average properties calculated by the 2-layer numerical specimen had large differences compared to the CLT results, which indicated that a caution must be needed when designig of thin plain weave composite structures.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.3
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• pp.58-64
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• 2003

Pogo is the instability resulting from the interaction between rocket structure and propulsion system of liquid propellant rocket. The coupling of structure and propulsion system can lead to severe problem in rocket. For the analysis of pogo, a time-invariant linearized mathematical model is developed for a selected flight time. Propulsion system is modeled using element representations for each components. Rocket structure is modeled using FEM. Form the results of modal analysis of structure, the behavior of structure can be represented. System equations for coupling structure and propulsion system are composed. The stability in obtained by the eigen solution of system matrix. The optimization of the design variables such as size, place of accumulator for suppressing pogo instability in carried out. This article of study can be used to determine the degree of stability, and guide the design of pogo suppression system.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.625-635
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• 1997

The base isolation technique and its benefits in reducing the transmitted earthquake energy into a structure have gained increasing recognition during the last two decades. Unfortunately, the current available design procedures, especially for base-isolated bridges, seem inadequate and too restrictive. As a result, practical design procedure still relies upon a series of deterministic time history analyses. In this study, the evaluation of the possibility of the normal mode method to predict the nonlinear seismic responses of base isolated bridges has been performed. The applicability has been examined through the numerical approach with isolator's elastic or plastic states of the base isolated bridges. Numerical results show that the 1st. mode period and the various responses are varied with the state but are conversed. And, the result show that the normal mode method is applicable to predict the seismic responses and to design the babe isolated bridge. Various analysis method to bridges with bilinearized hysteresis isolator and various pier heights are evalulated.