• 한국농공학회논문집
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• 제57권1호
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• pp.11-23
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• 2015

In this study the laboratory test for hydraulic conductivity and the seepage analysis with finite element method on measurement section of sea dike embankment were performed for the purpose of estimating the relative density of embankment from the measured pore water pressures, and both results of the test and the analysis were coupled with the method of estimating seepage blocking state with the hydraulic head loss rate in sea dike embankment. The relationship of void ratio vs hydraulic head loss rate was obtained by setting hydraulic conductivity as common ordinate on the relationships between the void ratio and the hydraulic conductivity and between the hydraulic conductivity and the hydraulic head loss rate. The void ratio on the segment between measuring points was calculated from the coupled relationship of the void ratio vs the hydraulic conductivity. The allowable upper and lower limits of hydraulic head loss rate and those of void ratio on the safety were generated from the coupled relationship between the laboratory compaction test and the sedimentation test. Current hydraulic head loss rate and void ratio were evaluated in the allowable range between upper and lower limits.

• 소성∙가공
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• 제16권2호
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• pp.126-131
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• 2007

Voids in a large rotor are formed in solidification process of a cast ingot. The voids have to be eliminated from the rotor by a forming process, because they would became stress-intensity factors which suddenly fracture the rotor in the operation. Previous studies on void-elimination of a large rotor have mainly focused on finding the process variables affecting the void-closure. But the study on the amount of void closure in a large rotor has been very rare. This study was performed to obtain an equation which predicts the amount of void-closure in a forging process of a large rotor and to evaluate the availability of the void-closure equation through finite element analyses. Firstly, 2D FE analysis was carried out to find effects of time integral of hydrostatic stress and effective strain on void volume rate of a large rotor in the upsetting process for various diameters and shapes of void, and material temperature. From the 2D FE analysis, we found that effective strain was suitable for predicting the void-closure of a large rotor, because there was a constant relationship between void volume rate and effective strain. And a void-closure equation was proposed fur predicting void-closure of a large rotor in the upsetting process. Finally, ken the 3D FE analysis, the proposed void-closure equation was verified to be useful for upsetting and cogging processes.

• 한국가시화정보학회지
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• 제18권1호
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• pp.11-17
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• 2020

The reduction of CO2 emissions has been a key target in the marine industry since the IMO's MEPC published its findings in 2009. Air lubrication method is one of the mature technologies for commercialization to reduce the frictional resistance and enhance fuel efficiency of ships. Since the air lubrication pattern varies according to the ship's standing position and injection flow rate, in order to effectively control the air lubrication system, it is necessary to be able to judge the air layer development state based on the information collected from the monitoring sensor. In this study, we performed the air lubrication ship simulation experiment to measure the void fraction and the frictional resistance. The void fraction was measured to confirm the behavior of the air. Through the measurement of the frictional resistance, the change in frictional resistance reduction rate from the injection point to the longitudinal direction of the ship was confirmed. Based on the measurement results, correlation analysis was performed on void fraction and frictional resistance reduction rate.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.313-327
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• 2019

Damage evolution in the form of void nucleation, propagation and coalescence is the primary cause that is responsible for the ductile failure of microalloyed steels. The Gurson-Tvergaard-Needleman (GTN) damage model has proven to be extremely robust for characterizing the microscopic damage behavior of ductile metals. Nonetheless, successful applications of the model on a given metal type are limited by the correct identification of damage parameters as well as the validation of the calculated void growth rate. The purpose of this study is two-fold. First, we aim to identify the damage parameters of the GTN model for Q345 steel (Chinese code), due to its extensive application in mechanical and civil industries in China. The identification of damage parameters is facilitated by the well-suited response surface methodology, followed by a complete analysis of variance for evaluating the statistical significance of the identified model. Second, taking notched Q345 cylinders as an example, finite element simulations implemented with the identified GTN model are performed in order to analyze their microscopic damage behavior. In particular, the void growth rate predicted from the simulations is successfully correlated with experimentally measured acoustic emissions. The quantitative correlation suggests that during the yielding stage the void growth rate increases linearly with the acoustic emissions, while in the strain-hardening and softening period the dependence becomes an exponential function. The combined experimental and finite element approach provides a means for validating simulated void growth rate against experimental measurements of acoustic emissions in microalloyed steels.

• Nuclear Engineering and Technology
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• 제24권2호
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• pp.168-177
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• 1992

이상유동 현상의 해석은 원자력 발전소의 각계통과 가압경수형 원자로의 안전성 분석, 각종 열 수력학적 현상의 해석 그리고 타 산업체의 필요성에 의해 그 연구의 중대성이 커지고 있다. 이러한 이상유동의 현상 해석에 있어서 국부적 영역에서의 기포계수 결정은 매우 중요하다. 본 연구에서는 이러한 이상유동시 국부적 기포계수의 측정을 위하여 원자로내 부수로를 모사한 수직사각 유로를 제작하였다. 또한 국부적 영역에서의 기포계수 측정에 적합한 것으로 알려진 전기탐침 및 그 부가회로를 제작하였으며, 완성된 탐침을 이용하여 실제 비등이 발생하는 실험용 유로내에서 국부적 기포계수의 측정을 시도하였다. 실험 결과 제작된 전기탐침 및 그부가회로의 타당성을 확인 할 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.703-706
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• 2005

This study is analyzed mechanical properties and durability of pavement of a road permeability porous concrete to mix polymer for the enhance of porous concrete of performance and durability. As a result, void ratio showed the tendency which the mixing rate of polymer is decreased a little as increased. And, the influence of void ratio according to the kind of polymer has the difference, but void ratio showed the tendency which the mixing rate of polymer is decreased a little as increased. Compressive strength showed the tendency which the mixing rate of polymer is increased a little as increased. but, it showed the tendency to be reduced rather when above $20\%$ it mixed polymer mixing rate $10\%$ at apex.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 봄 학술발표회 논문집
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• pp.177-184
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• 1999

In soft ground tunneling, shield method is very good for safety of neighboring structures. Although shield tunnel method has the merits to minimize the deformation of ground around tunnel, ground deformations occurred until the material grouted in tail void hardens are inevitable. In this study, the effects of micropile used as one method to restrain the settlement of neighboring structures by the tail void are studied by laboratory model tests. As a basic test result, the effective direction of micropile and the restraint rate of settlement by micropile reinforcement are known.

• Journal of Welding and Joining
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• 제24권3호
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• pp.42-48
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• 2006

Since the voids occur at the CD stud welds, the mechanism of void formation and void reduction method are investigated in this work. It is speculated that the voids are formed because of high short-circuit current above 1000A. When the simple flow model is used to estimate the void trapping condition, the most voids are trapped at the weld mainly due to fast cooling rate of the CD stud weld. Since it is almost impossible to remove the voids completely, a method is proposed to reduce the void by decreasing the short-circuit current at the end of the arcing time. The experimental results show that the void is reduced by decreasing the short-circuit current to 1000A.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2626-2631
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• 2007

Air-water two phase natural circulation flow in the T-HERMES (Thermo-Hydraulic Evaluation of Reactor cooling Mechanism by External Self-induced flow)-1D experiment has been evaluated to verify and evaluate the experimental results by using the RELAP5/MOD3 computer code. The RELAP5 results have shown that an increase in the coolant inlet area leads to an increase in the water circulation mass flow rate. However, the water outlet area does not effective on the water circulation mass flow rate. As the coolant outlet moves to a lower position, the water circulation mass flow rate decreases. The water level is not effective on the water circulation mass flow rate. As the height increases in the air injection part, the void fraction increases. However, the void fraction in the upper part of the air injector maintains a constant value. An increase in the air injection mass flow rate leads to an increase in the local void fraction, but it is not effective on the local pressure.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.406-409
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• 2005

In the forging operation of large ingot two break-down process are upsetting and cogging. The first purpose of upsetting is to ensure sufficient forging ratio for subsequent cogging operations and consolidate the voids along the centerline. The second purpose is related to improve the physical properties for a final product. Voids which are generated during the casting process can be one of the decisive defects of materials. So it is necessary to know the standard of Judgment for void-closure in upsetting operation. In practical conditions, FEM analysis(DEFORM 2D 8.1) was carried out to decide how much effective strain has influence on void-closure. It is finally suggested that the function consists of the effective strain of analysis data and the area rate of void.