• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.521-527
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• 2001

The dynamic performance analyses and tests for a 50kW turbo-generator (KIMM-TG50) were carried out. The operating concept of this machine is that it gets the initial driving force from the built-in motor-generator until it reaches its self-sustaining speed of 40,000 rpm, and then the driving mode is changed to self-operating mode by the combustor installed between the centrifugal compressor and the turbine. Due to winding mistake of motor-generator, the system could go only up to 22000 rpm by the motor so that high pressure air externally fed into the turbine was utilized to get the system to run up to 62,000 rpm thereafter. The vibration data collected during the tests revealed that the first bending critical speed is in near 5,600 rpm as predicted in the design stage of the rotor-bearing system, and that there were no other identifiable critical speeds up until 62,000 rpm due to high damping from the squeeze film damper-bearings supporting the rotor. This paper presented some of the experimental results along with dynamic performance predictions made in the design stage as a part of progress being made.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.353-362
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• 1999

This study is aimed to obtain the critical crack lengthes of the concrete gravity dam and to investigate variation of the effective stress intensity factors at the crack tips of multiple cracks. Applied loads are dynamic load composed of blast vibration and hydrodynamic pressure which can be considered in case of the blast work at near construction site, in addition to static load composed of hydrostatic pressure, crack pressure, and gravity load of the dam. The critical crack lengthes were calculated according to the crack locations, directions, and magnitudes of blast vibration. Also variation of the effective stress intensity factors with respect to the multiple crack shapes and distances between the crack tips was investigated.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10b
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• pp.317-323
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• 1987

A pressure tracking control of hydroforming processes, which is used in the precision forming of. sheet metals, is considered in this paper. The hydroforming of sheet metal is performed between the high-pressure chamber controlled by pressure control valve and the punch moving with constant speed. Since the pressure in the forming chamber is a critical factor to the quality of the product severely. It is important to control the pressure to follow a prescribed pressure trajectory, depending upon the material volume and shape of the parts to be formed. Taking into consideration of the volume chamge of forming chamber during the process and the nonlinearity of the electro-magnetic relief valve, a mathematical formulation of the model describing the dynamic characteristics of this model obtained. Based upon this model a PID controller is designed for the pressure tracking.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.20 no.1
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• pp.66-74
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• 2024

This study investigates the effects of temperatures and strain rates on the strength and ductility of Gr.91 (ASME Grade 91) steel which is widely being used as a heat-resistant material in Generation IV nuclear and super critical thermal power plants. The tensile behavior of modified 9Cr-1Mo (Gr.91) steel was studied for the three strain rates of 6.67×10^-5/s, 6.67×10^-4/s and 6.67×10-3/s over the temperature range from room temperature (RT) to 650℃. Experimental results showed that at specific combinations of temperatures (300~400℃) and strain rates, serrations appeared in the stress-strain curves. Concurrently, abnormal behaviors such as a plateau in yield strength and tensile strength, a minimum in ductility and negative strain rate sensitivity were observed. These phenomena were analyzed as significant characteristics of dynamic strain aging (DSA). Since this abnormal behavior in Gr.91 steel affects the material strength, it is judged that a correlation analysis between DSA and material strength should be crucial in the design and integrity evaluation of Gr. 91 steel pressure vessel and piping subjected to high-temperature loading.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.5
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• pp.353-363
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• 2017

The dynamics of a water-steam system in a once-through boiler was simulated based on the physics-based modeling approach, representing the system in response to large load change or scale disturbance simulations. The modeling considered the mass, energy conservation, and momentum equation in the water pipe and the focus was limited to the sub-critical pressure region. An evaporator tube modeling was validated against the reference data. A simplified boiler system consisting of economizer, evaporator, and superheater was constructed to match a 500 MW power boiler. The dynamic response of the system following a disturbance was discussed along with the quantitative response characteristics. The dynamic response of the boiler system was further evaluated by checking the case of an off-design point operation of the feedwater-to-fuel supply ratio. The results re-emphasized the significance of controlling the feedwater-to-fuel supply ratio and additional design requirements of the water-steam separator and spray attemperator.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.2
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• pp.1-8
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• 2019

The integrity of the Reactor Pressure Vessel (RPV) is affected by the neutrons bombarding the vessel wall leading to embrittlement. This irradiation-induced embrittlement leads to reduction in the fracture toughness of RPV materials. This paper presents a comparative study of typical Optimized Power Reactor (OPR)1000 reactor pressure-temperature (P-T) limit curves using the pre-2006 American Society of Mechanical Engineers (ASME) editions used in the power plant and the current ASME edition of 2010. The current ASME Code utilizes critical reference stress intensity factor based on the lower bound of static, while the Pre-2006 ASME editions are based the critical reference stress intensity factor based on the lower bound of static, dynamic and crack arrest. Model-Based Systems Engineering approach was used to evaluate ASME Code Section XI Appendix G for generating the P-T limit curves. The results obtained from this analysis indicate decrease in conservatism in P-T limit curves constructed using the current 2017 ASME code, which can potentially increase operational flexibility and plant safety. Hence it is recommended to use ASME code edition after 2006 be used in all operating nuclear power plants (NPPs) to establish P-T limit curve.

• Membrane and Water Treatment
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• v.9 no.4
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• pp.255-262
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• 2018

This study attempted to evaluate the process of self-forming dynamic membrane formation on mesh filter in membrane bioreactor with a two-stage method of batch (agitation) and continues (aeration) stage at different sludge concentrations. Four concentrations of activated sludge including $6{\pm}0.4$, $8{\pm}0.5$, $10{\pm}0.3$, $14{\pm}0.3g/L$ were used to demonstrate the optimal concentration of sludge for treating municipal wastewater and reducing fouling in dynamic membrane bioreactor. The formation time and effluent turbidity were decreased in the batch stage when increasing the activated sludge concentration. The minimum values of formation time and effluent turbidity were 14 min and 43 NTU for the optimum mixed liqueur suspended solids of $8{\pm}0.5g/L$, respectively. To improve operational condition and fouling reduction in the aeration stage, critical fluxes were measured for all concentrations by flux-step method. With increasing the sludge concentration, the relevant critical fluxes reduced. The optimum subcritical flux of $30L/m^2/h$ was applied as operating flux in the second stage. The maximum COD removal efficiency of 98% was achieved by the concentration of $8{\pm}0.5g/L$. Compressibility index of self-forming dynamic membrane and transmembrane pressure trend remained somewhat constant until the optimal concentration of $8{\pm}0.5g/L$ and thereafter they increased steeply.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.20-28
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• 2008

According to IAEA regulations, a transportation package of radioactive material should perform its intended function of containing the radioactive contents after the drop test, which is one of hypothetical accident conditions. Impact limiters attached to a transport cask absorb the most of impact energy. So, it is appreciated to determine properly the shape, size and material of impact limiters. A material data needed in this determination is a dynamic one. In this study, several materials considered as those of impact limiters were tested by a drop weight facility to acquire dynamic material characteristics data. Impact absorbing volume of the impact limiter was derived mathematically for each drop condition. A size optimization of impact limiter was conducted. The derived impact absorbing volumes were applied as constraints. These volumes should be less than critical volumes generated based on the dynamic material characteristics. The derived procedure to decide the shape of impact limiter can be useful at the preliminary design stage when the transportation package's outline is roughly determined and applied as input value.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.744-749
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• 2001

As related to rotordynamics, dynamic characteristics of the wear ring seal in high pressure multi-stage pump is calculated in the cases of labyrinth, damper and helically grooved types. The. results show that the labyrinth seal type has superior performance in the view point of leakage. However, in terms of rotordynamics view point, the damper seal type gains acceptable separate margin in critical speed range, while it has slightly inferior leakage performance compared to labyrinth seal type.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.546-549
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• 2004

The T-50/A-50 Golden Eagle was developed for a supersonic trainer and light combat aircraft. At the design stage, vibration control plans were established and applied. For cockpit vibration, crew comfort vibration level was defined by the requirement of MIL-A-8892. It is found that the T-50/A-50 meets the requirement of cockpit vibration from the flight test data analysis. This paper contains the results of cockpit vibration analysis using the flight test data and the results of human vibration analysis lot the pilot inside aircraft. The human vibration level of pilot is increased as dynamic pressure is increased and at the specific high dynamic pressure, the ride comfort indicates 'a little uncomfortable'. Overall analysis results show that the vibration level of T-50/A-50 cockpit is tolerable and not critical for pilot's comfort.