• Journal of Environmental Science International
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• v.3 no.1
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• pp.17-29
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• 1994

An one dimensional atmosphere-vegetation interaction model is developed to discuss of the effect of vegetation on heat flux in mesoscale planetary boundary layer. The canopy model was a coupled system of three balance equations of energy, moisture at ground surface and energy state of canopy with three independent variables of $T_f$(foliage temperature), $T_g$(ground temperature) and $q_g$(ground specific humidity). The model was verified by comparative study with OSUID(Oregon State University One Dimensional Model) proved in HYPEX-MOBHLY experiment. As the result, both vegetation and soil characteristics can be emphasized as an important factor iii the analysis of heat flux in the boundary layer. From the numerical experiments, following heat flux characteristics are clearly founded simulation. The larger shielding factor(vegetation) increase of $T_f$ while decrease $T_g$. because vegetation cut solar radiation to ground. Vegetation, the increase of roughness and resistance, increase of sensible heat flux in foliage while decrease the latent heat flux in the foliage.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.375-380
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• 2000

Experimental and numerical studies were done to investigate seismic performance of slender sheat wall with no boundary confinement. 1/3 scale-specimens that model the plastic region of long slender shear walls subjected to combined axial load and bending moment were rested to investigate strength, ductility, capacity of energy dissipation and strain distribution. The experimental results show that the slender walls fail due to early crushing in the compressive boundary, and then have very low ductility. The measured maximum compressive strain is 0.0021, which is much less then 0.004 being commonly used for estimation of ductility. The experimental results indicates that the maximum compressive strain is not a fixed value but is affected by moment gradient along the shear wall height and distance from neutral axis to the extreme compressive fiber.

• Nuclear Engineering and Technology
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• v.34 no.2
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• pp.132-141
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• 2002

The effects of microstructure on fretting wear were investigated in Inconel 690 tube. The microstructure observation indicated that the solution annealing temperature and time affected the grain size of the Inconel 690 tubes. The carbide morphology, along grain boundaries, was mainly affected by thermal treatment time and temperature. The wear test results showed that specimens with larger grain size and with coarse carbides along grain boundaries had better wear resistance. Cracks were found in specimens with carbides along the grain boundary, while few cracks were found in carbide free specimens. It seemed that the carbides on grain boundary assisted crack formation and propagation in carbide containing specimens. On the other hand, the micro-hardness of specimen did not have a major role in fretting wear. It could be inferred from the SEM images of worn surfaces that the main wear mechanism of carbide containing specimen was delamination, while that of carbide free specimen was abrasion.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.50-55
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• 2011

Energy resistance welding (ERW) is a pipe-producing process that has high productivity and low manufacturing cost. However, the high heat input of ERW degrades the mechanical property of the pipe. This study investigates the effect of heat input and alloying elements on microstructure and mechanical properties of ERW pipes. As the heat input increased, the ferrite amount increased. The ferrite amount in the weld centerline was larger than t at in the weld boundary. Medium carbon steels (S45C and K55) having 0.3~0.4wt.% carbon yielded a significant difference of ferrite amount in the weld centerline and weld boundary. High alloyed steels (DP780 and K55) having 1.5~1.6wt.% Mn showed a ferrite rich zone in the weld centerline. These phenomena are probably due to decarburization and demanganisation in the weld centerline. As the ferrite fraction increased, the hardness decreased a little for the S45C steels. In addition, DP780 steels and K55 steels showed that the hardness drops when those steels have a ferrite rich zone. But we demonstrated the good tensile property of the DP780 steels and K55 steels in which Mn is included.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.91-99
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• 2020

Post-installed anchors were widely used due to its workable benefits. Regarding the resistance performance of anchors, the critical edge distance is presented to minimize the impact of concrete splitting. In the case of actual anchors, however, it is difficult to obtain the ideal edge distance. The purpose of this study is to identify resistance performance and behavior characteristics that contain complex elements such as concrete crack occurring under tensile load. Tensile tests were conducted based on the standard method. Failure shape and the resistance characteristics that do not have the critical edge distance were derived by tensile load. Parametric analysis according to the boundary condition was performed to simulate the actual tensile behavior, through a nonlinear finite element model based on the specimen. Consequently therefore, verifying analysis results the resistance mechanism can be applied through boundary conditions.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.3
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• pp.335-342
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• 1999

The purpose of present research is to develop and efficient numerical method for the calculation of potential flow and predict the wave-making resistance for the application to ship design of tuna purse seiner. Havelock was considered the wave resistance of a post extending vertically downwards through the water from the surface, its section by a horizontal plane being the same at all depths and having its breadth small compared with its length. This enables us to elucidate certain points of interest in ship resistance. However, the ship has not infinite draft. So, the problem which is investigated ind detail in this paper is the wave resistance of a mathematical quadratic model in a uniform stream. The paper deals with the numerical calculation of potential flow around the series 60 with forward velocity by the new slender ship theory. This new slender ship theory is based on the asymptotic expression of the Kelvin-source, distributed over the small matrix at each transverse section so as to satisfy the approximate hull boundary condition due to the assumption of slender body. The numerical results using the panel shift method and finite difference method are compared with the experimental results for wigley mono hull. There are no differences in the wave resistance. However, it costs much time to compute not only wave resistance but also wave pattern over some range of Froude numbers. More improvements are strongly desired in the numerical procedure.

• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1338-1346
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• 2005

Effects of thermal contact resistance between heater and susceptor, susceptor and graphite board in a MOCVD reactor on temperature distribution and film growth rate were analyzed. One-dimensional thermal resistance model considering thermal contact resistance and heat transfer area was made up at first to find the temperature drop at the surface of graphite board. This one-dimensional model predicted the temperature drop of 18K at the board surface. Temperature distribution of a reactor wall from the three-dimensional computational fluid dynamics analysis including the gap at the wafer position showed the temperature drop of 20K. Film growth rates of InP and GaAs were predicted using computational fluid dynamics technique with chemical reaction model. Temperature distribution from the three-dimensional heat transfer calculation was used as a thermal boundary condition to the film growth rate simulations. Temperature drop due to the thermal contact resistance affected to the GaAs film growth a little but not to the InP film growth.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1635-1643
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• 2000

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.170-176
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• 2007

Iodine-induced stress corrosion cracking (ISCC) properties and the associated ISCC process of Zircaloy-4 and an Nb-containing advanced nuclear fuel cladding were evaluated. An internal pressurization test with a pre-cracked specimen was performed with a stress-relieved (SR) or recrystallized (RX) microstructure at $350^{\circ}C$, in an iodine environment. The results showed that the $K_{ISCC}$ of the SR and RX Zircaloy-4 claddings were 3.3 and 4.8MPa\;m^{0.5}, respectively. And the crack propagation rate of the RX Zircaloy-4 was 10 times lower than that of the SR one. The chemical effect of iodine on the crack propagation rate was very high, which was increased $10^4$ times by iodine addition. Main factor affecting on the micro-crack nucleation was a pitting formation and its agglomeration along the grain boundary. However, this pitting formation on the grain-boundary was suppressed in the case of an Nb addition, which resulted in an increase of the ISCC resistance when compared to Zircaloy-4. Crack initiation and propagation mechanisms of fuel claddings were proposed by a grain boundary pitting model and a pitting assisted slip cleavage model and they showed reasonable results.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.301-307
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• 2012

SiAlON glasses are silicates or alumino-silicates, containing Mg, Ca, Y or rare earth (RE) ions as modifiers, in which nitrogen atoms substitute for oxygen atoms in the glass network. These glasses are found as intergranular films and at triple point junctions in silicon nitride ceramics and these grain boundary phases affect their fracture behaviour. This paper provides an overview of the preparation of M-SiAlON glasses and outlines the effects of composition on properties. As nitrogen substitutes for oxygen in SiAlON glasses, increases are observed in glass transition temperatures, viscosities, elastic moduli and microhardness. These property changes are compared with known effects of grain boundary glass chemistry in silicon nitride ceramics. Oxide sintering additives provide conditions for liquid phase sintering, reacting with surface silica on the $Si_3N_4$ particles and some of the nitride to form SiAlON liquid phases which on cooling remain as intergranular glasses. Thermal expansion mismatch between the grain boundary glass and the silicon nitride causes residual stresses in the material which can be determined from bulk SiAlON glass properties. The tensile residual stresses in the glass phase increase with increasing Y:Al ratio and this correlates with increasing fracture toughness as a result of easier debonding at the glass/${\beta}-Si_3N_4$ interface.