• Coupled systems mechanics
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• v.7 no.3
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• pp.297-319
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• 2018

In this paper, the vibro-acoustic behaviors of vibrational cylindrical shells are investigated by using structural intensity approach. The reducing interior noise method for vibrating cylindrical shells is proposed by altering and redistributing the structural intensity through changing the damping property of the structure. The concept of proposed novel method is based on the properties of structural intensity distribution on cylindrical shells under different load and damping conditions, which can reflects power flow in the structures. In the study, the modal formulas of structural intensity are developed for the steady state vibration of cylindrical shell structures. The detailed formulas of structural intensity are derived by substituting modal quantities, in which the effect of main parameters such as weight coefficients and distribution functions on structure intensity are analyzed and discussed. Numerical simulations are first carried out based on the structural intensity analytical solutions of modal formulas. Through simulating the coupling vibration and acoustical radiation problems of cylindrical shell, the relationship between vibro-acoustic and structural intensity distribution is derived. We find that for cylindrical shell, by properly arranging damping conditions, the structural intensity can be efficiently changed and further the noise property can be improved. The proposed methodology has important implications and potential applications in the vibration and noise control of fuselage structure.

• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.104-112
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• 2002

Nowadays, many countries are interested in using CPS far navigation system of aircrafts, because it has technical and economic benefits. For the CPS based navigation system, the most important thing is reliability of the system. GPS navigation solution is very accurate. But when some faults are raised in the CPS navigation system of an aircraft, if they cannot be detected and alerts are not generated for pilots, the aircraft cannot be safe. So, I implemented an DGPS integrity monitoring system that detects faults of measurements and exclude the fault measurement from the satellite constellation used for calculating a navigation solution. This paper introduces 'the Least Square Residual Method' used to detect faults of measurements and the implemented real time integrity monitoring system using DGPS. To test the system, I operated the system under many different conditions. And from analysis of the data recorded, I could conclude that when the number of visible satellites was enough to detect faults, the system could detect the faults of measurements perfectly, isolate and exclude the fault measurement well. But for more reliable system, the measurement errors must be estimated more accurately and integrations of CPS and other instruments must be developed.

• Computers and Concrete
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• v.20 no.6
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• pp.731-738
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• 2017

Reinforced concrete flat plates consist of slabs supported directly on columns. The absence of beams makes these systems attractive due to advantages such as economical formwork, shorter construction time, less total building height with more clear space and architectural flexibility. Punching shear failure is usually the governing failure mode of flat plate structures. Punching failure is brittle in nature which induces more vulnerability to this type of structure. To analyze the flat plate behavior under punching shear, twelve finite element models of flat plate on a column with different parameters have been developed and verified with experimental results. The maximum range of variation of punching stress, obtained numerically, is within 10% of the experimental results. Additional finite element models have been developed to analyze the influence of integrity reinforcement, clear cover and column reinforcement. Variation of clear cover influences the punching capacity of flat plate. Proposed finite element model can be a substitute to mechanical model to understand the influence of clear cover. Variation of slab thickness along with column reinforcement has noteworthy impact on punching capacity. From the study it has been noted that integrity reinforcement can increase the punching capacity as much as 19 percent in terms of force and 101 percent in terms of deformation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1675-1680
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• 2010

Flow Accelerated Corrosion (FAC) occurring during in-service conditions results in localized wall-thinning in the feeder pipes of CANDU. The wall-thinning of the feeder pipes is the main degradation mechanisms affecting the integrity of piping systems. In this paper, we assess the integrity of wall-thinned feeder pipes by limit load analysis. The limit loads for wall-thinning feeder pipes subjected to in-plane bending and internal pressure were determined on the basis of finte element limit analyses. The limit loads are determined from the results of limit analyses of elasticperfectly-plastic materials using the large geometry change. Closed-form approximations of limit load solutions for wall-thinning feeder pipes subjected to in-plane bending and pressure are proposed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.2
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• pp.103-108
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• 2014

Growing concerns about environmental pollution have led to an increase in the demand for compressed natural gas (CNG) vehicles in recent years. CNG vehicles are equipped with a cylinder valve installed in a high-pressure vessel to control the CNG flow. The cylinder valve must meet high quality safety standards because the pressure vessel stores high-pressure CNG. Therefore, safety evaluation of the cylinder valve is necessary to ensure the safety of CNG vehicles. In this study, fluid-structure interaction analysis for the structural integrity of the cylinder valve were conducted using a commercial finite element analysis code(ANSYS WORKBENCH V14). The CFD analysis was performed using a steady-state technique according to the inlet and outlet pressures in order to predict the pressure distribution. Structural analysis was performed by a static structure technique at the maximum working pressure to evaluate the structural integrity of the cylinder valve. From the results, the safety factor of the valve component is between 1.57 and 21.5.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.7
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• pp.48-57
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• 2021

The main research content of this paper is to evaluate the structural integrity and the cooling performance of 4250 kVA power transformer with ONAN(Oil Natural and Air Natural) mode. The dynamic analysis is used to verify the structural safety of the transformer by seismic loading. The transformer structure is simplified and NX software is used to build a three-dimensional model, and ANSYS commercial software is used to calculate the stress and deformation by applying corresponding load. The analysis result was evaluated whether it satisfies the design requirements according to the IEEE Std 693 standard. In terms of thermal analysis to evaluate the cooling performance, the thermal physical model is used to calculate the heat exchange between the radiator and the tank in the steady state, and the result is input into the Fluent software to calculate the internal temperature field of the transformer tank, which reduces the calculation cost of thermal fluid. Comparing the simulated hot spot temperature and top oil temperature of the transformer with the calculation results of the IEC60076 classic model, it is found that the error is only 1.9%.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.487-495
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• 2005

Mechanical properties of in-service facilities are required to evaluate the integrity of power plants and chemical plants. Non-destructive technique can be used to evaluate the mechanical properties. To investigate the mechanical properties using ultrasonic technique, the four classes of thermally aged specimens were prepared using an artificially accelerated aging method. Ultrasonic tests, tensile tests, fracture toughness tests, and hardness tests were performed for the specimens. Then the mechanical properties were compared with ultrasonic parameters such as attenuation and non-linear parameter. From the investigation, we confirm that the ultrasonic parameter can be used to evaluate the mechanical properties.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.951-956
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• 2011

Inconel alloys are generally used as steam generator tubes in nuclear power plants. These alloys are highnickel chromium alloys that exhibit excellent resistance to aqueous corrosion. In this paper, the effects of elevated temperatures such as an operating temperature of $320^{\circ}C$ on the fretting fatigue behavior of inconel 600 and 690. We observed that the plain and fretting fatigue limits at $320^{\circ}C$ were slightly lower than those at room temperature. The frictional forces varied depending on the number of load cycles. After each test, we studied the fretting fatigue mechanisms via SEM observations. These results can be used for structural integrity evaluations at elevated temperatures and for studying fretting damage in steam generator systems.

• Corrosion Science and Technology
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• v.7 no.4
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• pp.224-232
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• 2008

During the hot rolling process, steels develop an oxide scale on their surface. This scale can affect the mechanical properties of the rolled steel and its surface aspect. The main problem comes from the mechanical integrity of the oxide scales which could delaminate or crack, leading eventually to later oxide incrustation within the steel. The objective of the present work is to qualify the mechanical integrity of the iron oxide scales during the hot rolling process. The laboratory experiments use a four point bending test to simulate the mechanical solicitation which takes place during the rolling sequence of the steel slabs. The oxide scales grow on a mild steel at $900^{\circ}C$ under wet or dry atmosphere and the oxidized steel is then mecahnically tested at $900^{\circ}C$ or $700^{\circ}C$. The high temperature four point bending tests are completed with microstructural observations and with the record of acoustic emission to follow in-situ the mechanical damages of the oxide scales. The results show the role of water vapor which promotes the scale adherence, and the role of the temperature as the oxide are more damaged at $700^{\circ}C$ than at $900^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1103-1108
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• 2012

A main steam pipe system is a branch pipe that connects a boiler with a turbine. Water hammering analysis is very important for limiting the damage caused to pipe systems by operation conditions. Water hammering created by an unsteady flow in pipeline systems can cause excessive change in pressure, vibration, and noise. The main steam pipe structure should be designed to safely maintain the pressure pulsation and several vibrations under operation environments. This study evaluated the structural integrity of a main steam pipe during suspended and normal operation by using the ASME fatigue life methodology and finite element analysis. In the analysis, water hammering was used for transient analysis. The calculated alternating stress and fatigue stress were compared with the applicable limits of ASME fatigue life. All the evaluation results satisfied the requirements of the ASME fatigue life.