• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.1-6
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• 1986

This paper presents a study on jet-flow-induced vibration, which has been one of the main causes of fuel damage in many pressurized water reactors. A systematic investigation was carried out experimently to identify the mechanism of jet-flow-induced vibration and to provide a design guide. Fluidelastic instability occurs when the jet velocity exceeds a critical value. The threshold of instability is given by V/f$_{n}$D=K.root.(D/h)(m$_{0}$.delta.$_{0}$/.sigma.D$^{2}$), where K is a stability constant. The effect of axial flow velocity and stand-off distance of a tube array on the stability of the array were investigated. A design guide is proposed.posed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.128-133
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• 2004

This study has been focused on the development of shear forming process of grid for lead-acid battery. The grid plays an important role in the flow of electricity because the grid is a skeleton of the pasted plate. Therefore, it must be of the highest quality to prevent plate failures and then, battery failure, and ensure the best battery performance possible. The finite element analysis of the shear forming process is carried out and the result is compared with the experimental data. The influence of the numerical parameters such as clearance, velocity of punch and critical damage value on the simulation results turns out to be very considerable.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.2 s.179
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• pp.81-87
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• 2006

This study has been focused on the analysis of high speed shear forming process for lead-acid battery grids. The grid plays an important role of electrical charge. It is necessary to ensure the best battery's performance that the grid should have a best quality. The clearance between punch and die, the velocity of punch and the critical damage value are very important parameters for making a good grid form. The finite element analysis of the shear forming process is carried out by measuring and optimizing these three important parameters. The result of this study concludes that these parameters has a great influence on grid quality.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.101-104
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• 2003

Influences of transverse compressive stress on the critical current ( $I_{c}$) in AgMg and AgMn alloy sheathed Bi-2223 tapes were investigated at 77 K and 0 T. The $I_{c}$ degradation behavior depending on sample specifications was discussed in viewpoints of n-value and damage morphology. As a result, Bi-2223 tapes showed a significant drop in $I_{c}$ for stresses greater than 50MPa. The AgMg sheathed Bi-2223 tapes representing higher $I_{c}$ showed a lower $\sigma$$_{irr}$ and a significant $I_{c}$ degradation with increase in compressive stress. There existed a voltage tap separation dependency of the $I_{c}$ degradation behavior caused by the transverse compressive stress.sive stress.s.

• Geomechanics and Engineering
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• v.33 no.1
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• pp.53-63
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• 2023

Rock disturbance caused by blasting and stress relaxation is commonly observed during excavation. As the distance from the source of disturbance increases, the degree of disturbance decreases, and rock at a large depth does not experience disturbance. However, in stability analyses, a single value of disturbance is often applied to the entire rock mass, which leads to underestimated results. In this study, this modeling mistake is addressed by considering realistically varying rock disturbance. The safety of infinite slopes in a disturbed rock mass with a strength governed by the Hoek-Brown failure criterion is investigated based on the kinematic approach of limit analysis. The maximum disturbance is assigned to the outermost slope face because it is directly exposed to blasting damage and dilation, and the disturbance progressively decays with distance in the rock mass. The safety analysis results indicate that the assumption of uniform disturbance in the entire rock mass leads to underestimation of the rock strength and safety on infinite rock slopes. A critical slip surface appears to be within the disturbed rock layer as well as the interface between the disturbed upper rock and undisturbed lower rock.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.5
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• pp.474-481
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• 2009

Fracture models and criteria of adhesive with two parameters, namely $G_C$ and ${\sigma}_{max}$, have been developed to describe the fracture process of adhesive joints. Cohesive zone model(CZM) is a representative two parameter failure criteria approach. In CZM, ${\sigma}_{max}$ is a critical, limiting maximum value of the stress in the damage zone ahead of the crack and is assumed to have some physical significance in adhesive failure. Based on CZM and finite element analysis method, the relationship between fracture load and adhesive properties, as $G_{IC)$ and $({\sigma}_{max})_I$, was investigated in adhesively bonded joint tensile test and T-peel test. The two parameters in tensile mode loading were evaluated by using the relationship. The value of $G_{\IC}$ evaluated by proposed method showed close agreement with analytical solution for tapered double cantilever beam(TDCB) test which proposed in an ASTM standard.

• The Journal of Internal Korean Medicine
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• v.22 no.4
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• pp.503-512
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• 2001

Objective : This study was carried out to investigate the effects of DDT on the brain damage and hypertension. Methods : We observed the effect of Dodamtang(DDT) extract on KCN-induced coma, focal brain ischemia by MCA occlusion, cytotoxicity and protection of PC12 cells and B103 cells induced by amyloid ${\beta}$ protein(25-35). To prove the effect of DDT as a blood pressure depressant, we measured aldosterone, renin activity, catecholamine, sodium and NO density using the seperated blood plasma. Results : DDT showed a protective effect on cytotoxicity of PC12 cells and B103 cells induced by amyloid ${\beta}$ protein(25-35) in a dose dependent manner and proved the significant abridgement of brain ischemic area and edema induced by MCA occlusion, a critical decrease of neurologic deficitic grade in the fore-limbs. DDT didn't reduce the duration of KCN(1.87mg/kg iv.)-induced coma and prolonged the survival rate in the case of KCN(3.0mg/kg iv.)-induced coma by the ratio of 20%. While DDT increased the value of NO in SHR, it significantly decreased the blood pressure of SHR and the value of aldosterone& epinephrine in SHR. Conclusions : These results suggested that DDT might be usefully applied for treatment of hypertension, cerebral infarction, and brain damage.

• Wind and Structures
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• v.29 no.3
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• pp.163-175
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• 2019

Multispan suspension bridges make a good alternative to single-span ones if the crossed strait or river width exceeds 2-3 km. However, multispan three-tower suspension bridges are found to be very sensitive to the wind load due to the lack of effective longitudinal constraint at their central tower. Moreover, at certain critical wind speed values, the aerostatic instability with sharply deteriorating dynamic characteristics may occur with catastrophic consequences. An attempt of an in-depth study on the aerostatic stability mode and damage mechanism of three-tower suspension bridges is made in this paper based on the assessment of strain energy and dynamic characteristics of three particular three-tower suspension bridges in China under different wind speeds and their further integration into the aerostatic stability analysis. The results obtained on the three bridges under study strongly suggest that their aerostatic instability mode is controlled by the coupled action of the anti-symmetric torsion and vertical bending of the two main-spans' deck, together with the longitudinal bending of the towers, which can be regarded as the first-order torsion vibration mode coupled with the first-order vertical bending vibration mode. The growth rates of the torsional and vertical bending strain energy of the deck after the aerostatic instability are higher than those of the lateral bending. The bending and torsion frequencies decrease rapidly when the wind speed approaches the critical value, while the frequencies of the anti-symmetric vibration modes drop more sharply than those of the symmetric ones. The obtained dependences between the critical wind speed, strain energy, and dynamic characteristics of the bridge components under the aerostatic instability modes are considered instrumental in strength and integrity calculation of three-tower suspension bridges.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.88-91
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• 2002

The two dimensional size effect of specimen gauge section (length x width) was investigated on the compressive behavior of a T300/924 [45/-45/0/90]3s, carbon fiber-epoxy laminate. A modified ICSTM compression test fixture was used together with an anti-buckling device to test 3mm thick specimens with a 30$\times$30, 50$\times$50, 70$\times$70, and 90mm$\times$90mm gauge length by width section. In all cases failure was sudden and occurred mainly within the gauge length. Post failure examination suggests that $0^{\circ}$ fiber microbuckling is the critical damage mechanism that causes final failure. This is the matrix dominated failure mode and its triggering depends very much on initial fiber waviness. It is suggested that manufacturing process and quality may play a significant role in determining the compressive strength. When the anti-buckling device was used on specimens, it was showed that the compressive strength with the device was slightly greater than that without the device due to surface friction between the specimen and the device by pretoque in bolts of the device. In the analysis result on influence of the anti-buckling device using the finite element method, it was found that the compressive strength with the anti-buckling device by loaded bolts was about 7% higher than actual compressive strength. Additionally, compressive tests on specimen with an open hole were performed. The local stress concentration arising from the hole dominates the strength of the laminate rather than the stresses in the bulk of the material. It is observed that the remote failure stress decreases with increasing hole size and specimen width but is generally well above the value one might predict from the elastic stress concentration factor. This suggests that the material is not ideally brittle and some stress relief occurs around the hole. X-ray radiography reveals that damage in the form of fiber microbuckling and delamination initiates at the edge of the hole at approximately 80% of the failure load and extends stably under increasing load before becoming unstable at a critical length of 2-3mm (depends on specimen geometry). This damage growth and failure are analysed by a linear cohesive zone model. Using the independently measured laminate parameters of unnotched compressive strength and in-plane fracture toughness the model predicts successfully the notched strength as a function of hole size and width.

• Journal of Wetlands Research
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• v.17 no.3
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• pp.237-244
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• 2015

This study is estimated the flood damage probability of the flood discharge, the flood stage estimation and Economic Analysis for Flood Control about considering of uncertainty. Sum River Basin has chosen and the probability precipitation is estimated by using the concept of critical rainfall duration depending on the frequency of each flood stage estimation point. For calculating the expected annual damage, the functions of long term hazard, discharge-frequency, stage-discharge and depth-damage are established for 8 areas in Sum River Basin. The expected annual damaged is obtained which is based on the sampling informations through more than 500,000 simulation from the functions of considered uncertainty. The result about the optimum frequency and Investment Priorities are estimated by conducting the evaluation about planning the levee of various of Design Frequency. In analysis result, 12% of B/C value has increased if the uncertainty has concerned. Also the optimum frequency or Investment Priorities are possible to be changed. If the political and social analysis perform together it would be helpful to have a reasonable decision other than only the economical analysis as actual Flood damaged reduction planning.