• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1611-1625
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• 2020

We propose a scaled-down experimental model of vertical air-natural convection channels by applying the modified Ishii-Kataoka scaling method with the assistance of numerical analyses to the Reactor Vault Cooling System (RVCS) of the Proto-type Gen-IV Sodium-cooled fast reactor (PGSFR) being developed in Korea. Two major non-dimensional numbers (modified Richardson and Friction number) from the momentum equation and Stanton number from the energy balance equation were identified to design the scaled-down experimental model to assimilate thermal-hydraulic behaviors of the natural convective air-cooling channel of RVCS. The ratios of the design parameters in the PGSFR RVCS between the prototype and the scaled-down model were determined by setting Richardson and Stanton number to be unity. The friction number which cannot be determined by the Ishii-Kataoka method was estimated by numerical analyses using the MARS-KS system code. The numerical analyses showed that the friction number with the form loss coefficient of 2.0 in the scale-down model would result in an acceptable prediction of the thermal-hydraulic behavior in RVCS. We also performed experimental benchmarking using the scaled-down model with the MARS-KS simulations to verify the appropriateness of the scale-down model, which demonstrated that the temperature rises and the average air flow velocity measured in the scale-down model.

• Polymer(Korea)
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• v.32 no.6
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• pp.598-602
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• 2008

In this study we prepared crosslinked separators with the improved thermal stability by irradiating a commercial polyethylene (PE) separator for lithium secondary battery with an electron beam, and the thermal and mechanical properties of the prepared separators were evaluated as a function of the absorption dose. The thermal shrinkage of electron beam irradiated separator was decreased with increasing absorption dose. As a result of the shutdown behavior using an AC impedance, it was observed that the irradiated separator had the better shutdown function than the unirradiated separator. The modulus of the irradiated separator was enhanced as the absorption dose was increased, while the tensile strength and the break elongation of the irradiated separator were decreased.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1152-1157
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• 2004

Temporal behavior of the laser induced incandescence (LII) signal is often used for soot particle sizing, which is possible because the cooling behavior of a laser heated particle is dependent on the particle size. In present study, LII signals of soot particles are modeled using two non-linear coupled differential equations deduced from the energy- and mass-balance of the process. The objective of this study is to see the effects of particle size, laser fluence on soot temperature characteristics and cooling behavior. Together with this, we focus on validating our simulation code by comparing with other previous results. Results of normalized LII signals obtained from various laser fluence conditions showed a good agreement with that of Dalzell and Sarofim's. It could be found that small particles cool faster at a constant laser fluence. And it also could be observed that vaporization is dominant process of heat loss during first 100ns after laser pulse, then heat conduction played most important role while thermal radiation had little influence all the time.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.181-184
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• 2008

Austenitic stainless steel is used as high temperature components such as gas turbine blade and disk because of its good thermal resistance. In the present investigation, tensile and low cycle fatigue behavior of 316 stainless steel was studied at wide temperature range $20^{\circ}C{\sim}750^{\circ}C$. In the tensile tests, it was shown that elastic modulus, yield strength, ultimate tensile strength decreases when temperature increased. The effect on fatigue failure of the parameters such as plastic strain amplitude and plastic strain energy density was also investigated. With the experimental results, a structural analysis of turbine blades of 316 stainless steel were carried out.

• Advances in concrete construction
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• v.13 no.2
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• pp.153-162
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• 2022

Prefabricated exterior wall panel is the main non-load-bearing component of assembly building, which affects the comprehensive performance of thermal insulation and durability of the building. It is of great significance to develop new prefabricated exterior wall panel with durable and lightweight characteristics for the development of energy-saving and assembly building. In the prefabricated sandwich insulation hanging wall panel, the selection of material for the outer layer and the arrangement of the connector of the inner and outer wall layers affect the mechanical performance and durability of the wall panels. In this paper, high performance cement-based composites (HPFRC) are used in the outer layer of the new type wall panel. FRP bars are used as the interface connector. Through experiments and analysis, the influence of the arrangement of connectors on the mechanical behaviors of thin-walled composite wall panel and the panel with window openings under two working conditions are investigated. The failure modes and the role of connectors of thin-walled composite wallboard are analyzed. The influence of the thickness of the wall layer and their combination on the strain growth of the control section, the initial crack resistance, the ultimate bearing capacity and the deformation of the wall panels are analyzed. The research work provides a technical reference for the engineering design of the light-weight thin-walled and durable composite sandwich wall panel.

• Steel and Composite Structures
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• v.45 no.3
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• pp.369-388
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• 2022

Composite effect between steel and recycled aggregate concrete (RAC) in steel reinforced-RAC (SRRAC) structures can effectively improve RAC's adverse mechanical properties due to the natural defects of recycled coarse aggregate (RCA). However, the performance of SRRAC after thermal exposure will have a great impact on the safety of the structure. In this paper, firstly, the mechanical properties of SRRAC structures after high temperatures exposure were tested, including 24 SRRAC columns and 32 SRRAC beams. Then, the change rules of beams and columns performance with the maximum temperature and replacement percentage were compared. Finally, the formulas to evaluate the residual bearing capacity of SRRAC beams and columns after exposure to high temperatures were established. The experimental results show that the maximum exposure temperature can be judged by the apparent phenomenon and mass loss ratio of RAC. After high temperatures exposure, the mechanical properties of SRRAC beams and columns change significantly, where the degradation of bearing capacity and stiffness is the most obvious. Moreover, it is found that the degradation degree of compression member is more serious than that of flexural member. The formulas of residual bearing capacity established by introducing influence coefficient of material strength agree well with the experimental results.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.6
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• pp.495-502
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• 2014

Glass-reinforced polyurethane foam (R-PUF) is widely used as the primary and secondary insulation of Mark-III type liquefied natural gas (LNG) cargo system. And, polyurethane foam (PUF) and polyisocyanurate foam (PIR) are often used for insulation of onshore structures or LNG storage and pipeline system. These polymeric foam materials are known for the characteristics that mechanical properties are dependent on strain rate and temperature. In this study, compression tests for R-PUF, PIR, and PUF were carried out for the estimation of mechanical behaviors under the cryogenic environment. The range of thermal condition was from room temperature to 110K and strain rates were $10^{-3}s^{-1}$ and $10^{-4}s^{-1}$. The test results were analyzed based on the conditions of strain-rate and temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.9
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• pp.859-866
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• 2010

Nonlinear dynamics of pulsating instability-diffusional-thermal instability with Lewis numbers sufficiently higher than unity-in counterflow diffusion flames, is numerically investigated by imposing a Damkohler number perturbation. The flame evolution exhibits three types of nonlinear behaviors, namely, decaying pulsating behavior, diverging behavior (which leads to extinction), and stable limit-cycle behavior. The stable limit-cycle behavior is observed in counterflow diffusion flames, but not in diffusion flames with a stagnant mixing layer. The critical value of the perturbed Damkohler number, which indicates the region where the three different flame behaviors can be observed, is obtained. A stable simple limit cycle, in which two supercritical Hopf bifurcations exist, is found in a narrow range of Damkohler numbers. As the flame temperature is increased, the stable simple limit cycle disappears and an unstable limit cycle corresponding to subcritical Hopf bifurcation appears. The period-doubling bifurcation is found to occur in a certain range of Damkohler numbers and temperatures, which leads to extend the lower boundary of supercritical Hopf bifurcation.

• Structural Engineering and Mechanics
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• v.71 no.5
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• pp.485-502
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• 2019

In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton's principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.543-567
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• 2016

This study attempts to address the buckling and free vibration characteristics of an isotropic cylindrical panel subjected to non-uniform temperature rise using numerical approach. Finite element analysis has been used in the present study. The approach involves three parts, in the first part non-uniform temperature field is obtained using heat transfer analysis, in the second part, the stress field is computed under the thermal load using static condition and, the last part, the buckling and pre-stressed modal analysis are carried out to compute critical buckling temperature as well as natural frequencies and associated mode shapes. In the present study, the effect of non-uniform temperature field, heat sink temperatures and in-plane boundary constraints are considered. The relation between buckling temperature under uniform and non-uniform temperature fields has been established. Results revealed that decrease (Case (ii)) type temperature variation field influences the fundamental buckling mode shape significantly. Further, it is observed that natural frequencies under free vibration state, decreases as temperature increases. However, the reduction is significantly higher for the lowest natural frequency. It is also found that, with an increase in temperature, nodal and anti-nodal positions of free vibration mode shapes is shifting towards the location where the intensity of the heat source is high and structural stiffness is low.