• Tunnel and Underground Space
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• v.24 no.1
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• pp.67-80
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• 2014

Long-term stability and delayed failure of granite were evaluated through the laboratory test based on Wilkins method and Brazilian disc test (BDT) which yields tensile strength, mode I fracture toughness and subcritical crack growth parameters. Then, the long-term strength of granite was estimated by using analytical models and long-term stability of compressed air-energy storage (CAES) pilot cavern pressurized up to 5 ~ 6 MPa was evaluated using numerical code, FRACOD with the determined subcritical crack growth parameters. The results of test and analyses showed that the subcritical crack growth index, n was determined as 29.39 and the inner pressure of 5 ~ 6 MPa had an insignificant effect on the long-term stability of pilot cavern. It was also found that the measurement and analysis of acoustic emission events can describe the accumulation of damage due to subcritical crack growth quantitatively. That is, AE monitoring can provide the current status of rock under loading if we make an identical installation condition in the field with that of the laboratory test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.85-90
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• 2010

Friction welding is a common practice to join axially symmetrical parts for automobile industry applications. The shaft for automobile reverse idle gear is generally produced by forging steel, SF 45. This method is not so good because of high cost of material and production. In this study, in order to investigate the possibility of application of SM 45C to SF 45 dissimilar friction welding, the dissimilar friction welded joints were performed using 20 mm diameter solid bar in forging steel(SF 45) to carbon steel(SM 45C). The optimal friction welding parameters were selected to ensure reliable quality welds on the basis of visual examination, tensile test, micro-Virkers hardness surveys of the bond of area and optical microstructure investigations for welded joint parts. Finally, post weld heat treatment(PWHT) of the high-frequency induction hardening was performed for the friction welded specimens under the optimal welding conditions. And then, the mechanical properties were compared for as-welded and PWHT in SM 45C to SF 45.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.5
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• pp.518-527
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• 2016

The present study considers the usage of concentrated forces to simulate real panel flutter. The concept of using concentrated forces have been validated for studying the flutter of wing structure in subsonic flow, yet its application in the supersonic region remained to be explored. Hence, a simply supported panel subjected to forces, equivalent to aerodynamic force is considered for studying supersonic panel flutter. The distributed aerodynamic forces are approximated to few concentrated forces by taking numerical integration. The aeroelastic equation is formulated using the classical small-deflection theory and the piston theory for linear panel flutter whereas for emulated panel flutter the flutter equation is derived by replacing the pressure due to aerodynamic loading with pressure from concentrated loading. Finally, flutter frequency, flutter dynamic pressure, and corresponding mode shape are found for emulated panel flutter and compared with linear panel flutter. Two important parameters, the number of concentrated forces and their location are discussed through numerical examples and optimization process respectively. So far, the flutter results acquired in this study are reasonable to suggest the feasibility of reproducing panel flutter using concentrated forces.

• Tunnel and Underground Space
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• v.23 no.6
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• pp.493-505
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• 2013

This numerical study investigates seismicity and fault slip induced by fluid injection in deep geothermal reservoir with pre-existing fractures and fault. Particle Flow Code 2D is used with additionally implemented hydro-mechanical coupled fluid flow algorithm and acoustic emission moment tensor inversion algorithm. The output of the model includes spatio-temporal evolution of induced seismicity (hypocenter locations and magnitudes) and fault deformation (failure and slip) in relation to fluid pressure distribution. The model is applied to a case of fluid injection with constant rates changing in three steps using different fluid characters, i.e. the viscosity, and different injection locations. In fractured reservoir, spatio-temporal distribution of the induced seismicity differs significantly depending on the viscosity of the fracturing fluid. In a fractured reservoir, injection of low viscosity fluid results in larger volume of induced seismicity cloud as the fluid can migrate easily to the reservoir and cause large number and magnitude of induced seismicity in the post-shut-in period. In a faulted reservoir, fault deformation (co-seismic failure and aseismic slip) can occur by a small perturbation of fracturing fluid (<0.1 MPa) can be induced when the injection location is set close to the fault. The presented numerical model technique can practically be used in geothermal industry to predict the induced seismicity pattern and magnitude distribution resulting from hydraulic stimulation of geothermal reservoirs prior to actual injection operation.

• Journal of the Korea Fashion and Costume Design Association
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• v.23 no.3
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• pp.1-10
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• 2021

Harnesses are used in a variety of industries, such as rescue operations, medicine, and entertainment. However, conventional harnesses have problems as they are uncomfortable to wear and causes continuous pain. Therefore, in this study, the load and pressure applied to the body in the flying state when using a conventional harness were measured in real time and the distribution change was observed. Load and pressure were measured using a modified corset harness, a pressure sensor, and a human mannequin to measure the maximum and average pressure on the waist. As a result, it was confirmed that the load concentrated on the waist in the flying state was 104 N, and the pressure was applied to the left and right sides was 800 kPa or greater. The pressure distribution showed a pressure of 3-45 kPa in 73% in all measurable pressures. The results of the load and pressure distribution are presented as basic data for improving the wearability and reducing the discomfort of harnesses in the future, aid in the development of a harnesses that can minimize discomfort for various activities, and increase the concentration on experiential activities. In addition, using the CLO 3D program, which is a 3D virtual wearing system, a harness was put on a virtual model, and the compression level was checked and compared with the actual pressure distribution. As a result of comparing the measured pressure values in the flying state with the clothing pressure wearing the harness in the CLO 3D program, the total pressure value was found to be about 68% of the actual measured value. This helps develop a harness that can minimize discomfort during activities by predicting the load and pressure on the body by first applying new designs to a virtual wearing system during development. These new harness patterns can solve the problems of conventional harnesses.

• Journal of the Korean Geosynthetics Society
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• v.12 no.4
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• pp.87-98
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• 2013

This study was performed a series of the isotropic compression-expansion tests and the drained triaxial tests with various the relative densities 40%, 60%, 80% and 95% for bottom ash. Using the tests results the characteristic of the parameters of Lade's single hardening constitutive model were investigated. The soil parameters Kur and n representing elastic behavior are not much affected by the change of the relative density. The other parameters such as failure criterion(m, ${\eta}_1$), hardening function(c, p) and plastic potential(${\psi}_2$, ${\mu}$) are in a positive linear relationship with the relative density. Since the soil parameters h and ${\alpha}$ representing yield function do not change much to the change of relative density and also closely related to failure criterion, they can be replaced by failure criterion ${\eta}_1$. We also observed that predicted values from the Lade's single hardening constitutive model were well consistent with the observed data.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.24-29
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• 1998

An experimental study was carried out to investigate the characteristics of spray pattern such as discharge coefficient, spray angle, and mass distribution for two-fluid airblast swirl injector, within the range of fluid supply pressure 0~13kg/$\textrm{cm}^2$. In general atomization is promoted with increasing total gas mass flow and performance of the splay pattern was more stable when radial mass flow was greater than axial mass flow, radial swirler was better than Axial swirler for atomization. Equivalent spray angle did not change with water mass flow except for the condition of 3kg/$\textrm{cm}^2$ and showed the same for the gas mass flow. Mass distribution from the patternator shows that maximum value of the distribution were lowered but distributed larger area when gas flow rate increased. Center of mass position did not change with increasing water mass flow.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.72-79
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• 1987

In this paper, an investigation of the property of blended fuel oil, combustion characteristics and engine performance was made, in case blended fuel oil(light oil+heavy oil) was used in a home-made precombustion diesel engine for small-sized fishing boat. The results may be summarized as follows: 1. The specific gravity was linearly increased in accordance with the increase in heavy oil ratio in blended fuel oil, and the relationship between viscosity and temperature was coincided with the formula of Walther-ASTM, and the CCAI, the ignition quality index, was increased nearly as a straight line of the gradient 1.0. 2. The ignition delay was slightly increased below 810 of CCAI(blending ratio to be 60% of heavy oil), but remarkably increased above 810 of CCAI. Therefore, it was considered that the practicable value of CCAI, ignition quality of blended fuel oil, was more than 810. 3. The maximum combustion pressure was increased until blending ratio of heavy oil was raised up to 40%. On the contrary, it came to be decreased at that ratio, with smoke emissions remarkably increasing above 60%. Therefore, it was found in this experiment that the best practicable limit of heavy oil blending ratio was around 50% for saving fuel costs with least smoke emissions.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.26-26
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• 1987

In this paper, an investigation of the property of blended fuel oil, combustion characteristics and engine performance was made, in case blended fuel oil(light oil+heavy oil) was used in a home-made precombustion diesel engine for small-sized fishing boat. The results may be summarized as follows: 1. The specific gravity was linearly increased in accordance with the increase in heavy oil ratio in blended fuel oil, and the relationship between viscosity and temperature was coincided with the formula of Walther-ASTM, and the CCAI, the ignition quality index, was increased nearly as a straight line of the gradient 1.0. 2. The ignition delay was slightly increased below 810 of CCAI(blending ratio to be 60% of heavy oil), but remarkably increased above 810 of CCAI. Therefore, it was considered that the practicable value of CCAI, ignition quality of blended fuel oil, was more than 810. 3. The maximum combustion pressure was increased until blending ratio of heavy oil was raised up to 40%. On the contrary, it came to be decreased at that ratio, with smoke emissions remarkably increasing above 60%. Therefore, it was found in this experiment that the best practicable limit of heavy oil blending ratio was around 50% for saving fuel costs with least smoke emissions.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.175-183
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• 1999

Recently, problems related to vibrations of decomposed granite soils have acquired increasing attention in Korea because those soils cover approximately one third of the country. Both resonant column and cyclic triaxial test were performed to investigate deformation characteristics of unsaturated and cement-mixed decomposed granite soils in Suwon region. The important soil parameters in this respect are the shear moduli, dynamic moduli of elasticity and damping ratios. The dynamic parameters are influenced by variables such as strain amplitude, ratio of loading cycles, and degree of saturations, etc. Test results and data have shown that the optimum degree of saturation to the maximum shear modulus due to a capillary menisci effect was about 17~18 % at low strain amplitude and 10~15 % at intermediate strain amplitude. This paper suggests the range of threshold strain and mean shear modulus of decomposed granite soils in Suwon region. It also proposed the empirical relationship between the dynamic parameters for cement-mixed and non-mixed decomposed granite soils.