• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.3
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• pp.142-154
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• 2011

This study predicted the probability of corrosion initiation of reinforced concrete tunnel boxes structures using the Monte Carlo Simulation. For the inner wall and outer wall in the tunnel boxes, exposed to airborne chloride ion and seawater directly respectively, statistical values of parameters like diffusion coefficient D, surface chloride content $C_s$, cover depth c, and the chloride threshold level $C_{lim}$ were examined from experiment or literature review. Their average values accounted for $3.77{\times}10^{-12}m^2/s$, 3.0% by weight of cement, 94.7mm and 45.5mm for outer wall and inner wall, respectively, and 0.69% by weight of cement for D, $C_s$, c, and $C_{lim}$, respectively. With these parametric values, the distribution of chloride contents at rebar with time and the probability of corrosion initiation of the tunnel boxes, inner wall and outer wall, was examined by considering time dependency of chloride transport. From the examination, the histogram of chloride contents at rebar is closer to a gamma distribution, and the mean value increases with time, while the coefficient of variance decreases with time. It was found that the probability of corrosion initiation and the time to corrosion were dependent on the time dependency of chloride transport. Time independent model predicted time to corrosion initiation of inner wall and outer wall as 8 and 12 years, respectively, while 178 and 283 years of time to corrosion was calculated by time dependent model for inner wall and outer wall, respectively. For time independent model, the probability of corrosion at 100 years of exposure for inner wall and outer wall was ranged 59.5 and 95.5%, respectively, while time dependent model indicated 2.9 and 0.2% of the probability corrosion, respectively. Finally, impact of $C_{lim}$, including values specified in current codes, on the probability of corrosion initiation and corrosion free life is discussed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.241-250
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• 1990

Characteristic relaxation time and characteristic diffusion time of viscoelastic fluids are determined experimentally by measuring the zero-shear-rate viscosity by falling ball viscometer and the infinite-shear-rate viscosity by capillary tube viscometer. Fluids used in experiments are aqueous solutions of polyacrylamide Separan AP-273 and the polymer concentrations range from 300 to 2000 wppm. A newly designed laser beam and timer system is employed to overcome the difficulty in measuring terminal velocities of the low concentration solutions. Ball removal device is prepared to remove the dropped ball from the bottom of cylinder without disturbing the testing fluid. In order to measure the zero-shear-rate viscosity, densities of hollow aluminium balls are adjusted very close to the densities of testing fluids. Characteristic diffusion time, which is ball viscometer. However, terminal velocity of a needle by falling ball viscometer is not affected by the time interval of dropping needles and characteristic diffusion time is not measured with a dropping needle. Powell-Eyring model predicts the highest values of the characteristic relaxation times among models used for heat transfer experimental works for a given polymer solution. As degradation of a polymer solution continues, the zero-shear-rate viscosity decreases more seriously than the infinite-shear-rate viscosity. Characteristic relaxation times of polymer solutions decreases as degradation continues.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.1-7
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• 2017

Concrete behavior in early-age is changing due to hydration reaction with time, and a resistance to chloride attack and strength development are different characterized. In the present work, changing strength and resistance to chloride attack are evaluated with ages from 28 days to 6 months. For the purpose, strength, diffusion coefficient, and passed charge are evaluated for normal concrete with 3 different mix proportions considering 28-day and 6-month curing conditions. With increasing concrete age, the changing ratio of strength falls on the level of 135.3~138.3%, while diffusion coefficient and passed charge shows 41.8%~51.1% and 53.6%~70.0%, respectively. The results of chloride diffusion coefficient and passed charge show relatively similar changing ratios since they are much dependent on the chloride migration velocity in electrical field. The changing ratios in chloride behaviors are evaluated to be much larger than those in compressive strength since the ion transport mechanism is proportional to not porosity but square of porosity.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.280-281
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• 2008

전력시스템 전자기 과도현상은 시간 영역에서 정확하고 효과적으로 해석되어져야 한다. 그러나 대규모 전력시스템을 상세하게 표현하기 위해서는 엄청난 계산량이 필요하다. 따라서 전력시스템 과도현상을 해석하기 위하여 전력시스템의 작은 부분은 상세하게 표현하고, 나머지 부분은 효과적으로 등가 시스템이 필요하다. 본 논문에서는 모든 주파수 영역에서 등가 시스템을 개발하기 위하여 벡터 적합을 이용하여 S 영역 유리함수 계수를 추정하고, 과거항과 순간항을 고려한 주파수 의존 등가 시스템을 개발하였다. 개발한 FDNE의 우수성을 입증하기 위하여 테스트 시스템에 적용하여 시스템이 고장시 전자기 과도현상을 비교, 검토하였다.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.3
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• pp.189-196
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• 1992

To know the extension effect of storage temperature on the pre-rigor period of plaice, Paratichthys olivaceus muscle, the relationship between early changes after death and temperature dependency was studied. Killed plaices instantly with spiking at the brain were stored at $-3^{\circ}C,\;0^{\circ}C,\;5^{\circ}C\;and\;10^{\circ}$ used in studying the changes in rigor Index, ATP and its related compounds, lactate contents and K-value. The most shortest onset time of rigor-mortis and full rigor was revealed in the sample stored at $-3^{\circ}C$ among the all samples, where rigor-mortis began at 4hrs after spiking and maximum tension was attained after 28hrs. However, in case of fresh plaice muscle stored at $10^{\circ}C$, the onset of rigor-mortis and full rigor were retarded to 14hrs and 52hrs after spiking. ATP in sample stored at $5^{\circ}C\;and\;10^{\circ}C$ were decomposed slowly than sample at $0^{\circ}C\;-3^{\circ}C $ and within 35hrs storage. The fastest rate and the maximum content of lactate accumulation were showed in sample stored at $-3^{\circ}$ among the all samples. The correlation coefficient(r) between the rate of rigor mortis and ATP breakdown, rigor mortis and lactate accumulation, and ATP breakdown and lactate accumulation were -0.981946, 0.965044, and -0.964728, respectively. Freshness of $-3^{\circ}C$ stored samples was maintained for the longest time compared with other stored samples. The times reached around $20\%$ of K-value were 240hrs for samples stored at $-3^{\circ}C,\;96hrs\;for\;0^{\circ}C\;samples,\;71hrs\;for\;5^{\circ}C\;samples,\;and\;22hrs\;for\;10^{\circ}C$ samples. Samples stored at $-3^{\circ}C,\;and\;0^{\circ}C$ were showed higher temperature dependency on rate of rigor-mortis, ATP breakdown, and lactate accumulation than $5^{\circ}C\;and\;10^{\circ}C$ stored samples, but those samples have a lower temperature dependency on K-value.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.667-674
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• 2011

This paper discusses the analysis method of prestressed concrete girder integral abutment bridges for a 75-year bridge life and the development of prediction models for abutment displacements under thermal loading due to annual temperature fluctuation and time-dependent loading. The developed nonlinear numerical modeling methodologies considered soil-structure interaction between supporting piles and surrounding soils and between abutment and backfills. Material nonlinearity was also considered to simulate differential rotation in construction joints between abutment and backwall. Based on the numerical modeling methodologies, a parametric study of 243 analysis cases, considering five parameters: (1) thermal expansion coefficient, (2) bridge length, (3) backfill height, (4) backfill stiffness, and (5) pile soil stiffness, was performed to established prediction models for abutment displacements over a bridge life. The parametric study results revealed that thermal expansion coefficient, bridge length, and pile-soil stiffness significantly influenced the abutment displacement. Bridge length parameter significantly influenced the abutment top displacement at the centroid of the superstructure, which is similar to the free expansion analysis results. Developed prediction model can be used for a preliminary design of integral abutment bridges.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.2
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• pp.116-126
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• 2003

In this study, a method that leads to make a simple decision on important parameters in analysis of wave field in permeable rubble-mound, block-mound breakwater, such as penetration velocity of incident waves and resistance coefficient, is introduced. A model that could analyze wave field of permeable breakwater in harbor, by applying these methods and arbitrary transmission coefficient boundary condition to a time-dependent mild-slope equation, was introduced. The verification of the model was done by carrying out 2-D physical model test on permeable breakwater, measuring the change in water surface elevation, comparing the computation result with time series, and comparing the result gained from the 3-D physical model test on permeable block-mound breakwater in an field harbor with the computation result in terms of regional wave height ratio in a harbor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.851-858
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• 2010

A generalized elastic solution for a transient mode III crack propagating along the gradient in functionally graded materials (FGMs) is obtained through an asymptotic analysis. The shear modulus and density of the FGMs are assumed to vary exponentially along the gradient. The stress and displacement fields near the crack tip are obtained in terms of powers of radial coordinates, and the coefficients depend on the time rates of the change of the crack tip speed and stress intensity factors. The influence of nonhomogeneity and transients on the higher order terms of the stress and displacement fields is discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.501-510
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• 2000

Recently, advanced signal analysis which is called "time-frequency analysis" has been used widely in nondestructive evaluation applications. Wavelet transform(WT) and Wigner Distribution are the most advanced techniques for processing signals with time-varying spectra. Wavelet analysis method is an attractive technique for evaluation of material characterization nondestructively. Wavelet transform is applied to the time-frequency analysis of ultrasonic echo waveform obtained by an ultrasonic pulse-echo technique. In this study, the feasibility of noise suppression of ultrasonic flaw signal and frequency-dependent ultrasonic group velocity and attenuation coefficient using wavelet analysis of ultrasonic echo waveform have been verified experimentally. The Gabor function is adopted the analyzing wavelet. The wavelet analysis shows that the variations of ultrasonic group velocity and attenuation coefficient due to the change of material characterization can be evaluated at each frequency. Furthermore, to assure the enhancement of detectability and naw sizing performance, both computer simulated results and experimental measurements using wavelet signal processing are used to demonstrate the effectiveness of the noise suppression of ultrasonic flaw signal obtained from austenitic stainless steel weld including EDM notch.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.1
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• pp.30-36
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• 1992

In order to measure the characteristics of Surface Acousitc Wave(SA W) with compositions of $LiNbO_3$ single crystal, $128^{\circ}$ Y cut wafer was fabricated from $LiNbO_3$ single crystals with the composition range of 47-50 $Li_2O$mol%. Delay lines were formed on the $128^{\circ}$ Y cut wafer using photolithography technique. Delay time was measured by pulse-echo overlap method. The compositional dependence of SAW characteristics, SAW velocity, electro-mechanical coupling coefficient$(K_s^2)$ and temperature coefficient of delay time(TCD), were investigated.