• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1195-1207
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• 1998

Periodic pulsations in the static pressure near turbine surfaces as blade rows move relative to each other is one of the important sources of turbine unsteadiness. The present experiment aims to investigate the effect of the static pressure pulsations on the interaction of film coolant flows from two rows of staggered holes with mainstream and its effect on film cooling heat transfer. Potential flow pulsations are generated by the rotating shutter mechanism installed downstream of the test section, The free-stream Strouhal number based on the boundary layer thickness is in the range of 0.033 - 0.33, and the amplitude of about 10-20%. Measured are time-averaged and phase-averaged velocity variations, pressure variations and temperature distributions of the flow field. Experimental conditions are identified by boundary layer measurements. Injectant behavior is characterized by the measurements of unsteady pressure in the plenum chamber and free-stream static pressure. The film cooling effectiveness is evaluated from the insulated wall temperature measurement. It has been found that bulk flow pulsation provides very large diffusion of the injectants and the effectiveness is significantly reduced by the flow pulsations.

• Wind and Structures
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• v.27 no.6
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• pp.417-430
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• 2018

The concentration fields in the proximities of a local gas emission source are experimentally analyzed in several combinations of wind incidences and source emissions. These conditions are determined by the plume buoyancy, emission velocity and incident flow wind speed. Concentration measurements are performed by an aspirating probe in a boundary layer wind tunnel. The analysis included the mean concentration values and the intensity of concentration fluctuations in a neutral atmospheric boundary layer flow. Different configurations are tested: an isolated stack in a homogeneous terrain and a stack with a bluff body in close proximity, located windward and leeward from the emission source. The experimental mean concentration values are contrasted with Gaussian profiles and the dilution factor is analyzed with respect to the empirical curves of the minimum dilution. Finally, a study on the plume intermittency is performed in a cross-sectional plane near the emission source. It is possible to highlight the following observations: a) plume vertical asymmetry in the case of an isolated emission source, b) significant differences in the dispersion process related to the relative location of the emission source and bluff body effects, and c) different probabilistic behavior of the concentration fluctuation data in a cross-sectional measurement plane inside the plume.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.908-917
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• 1995

The constant .DELTA.K fatigue tests are performed in SS41 and its weldments to investigate crack opening behavior and fatigue crack propagation behavior at each parts of weldment and its boundary layer. The weldments were annealed after welding for the purpose of relieving residual stress. Every weldments has notch at weld metal zone, and fatigue crack propagates from weld metal zone to vase metal zone perpendicular to weld line. The Laser ISDG method is used in order to determine the crack opening ratio, this method is more precise than indirect measurement method, and faster and easier than other direct measurement method.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.240-248
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• 2008

The effect of alloying elements(Mn, S, Mo, B) on the high temperature deformation behavior of Fe-29%Ni-17%Co (Kovar) alloy were investigated. And the effect of high temperature oxidation on the hot ductility was also studied. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and lowering of S content. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the FeS sulfide along the grain boundary. When Mn was added, the type of sulfide was changed to MnS from FeS and ductile intergranular fracture and transgranular fracture were promoted. The formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. Hot ductility was remarkably improved by the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range ($900{\sim}1000^{\circ}C$).

• Tunnel and Underground Space
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• v.12 no.3
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• pp.171-178
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• 2002

A dynamic analysis of a horseshoe_shaped tunnel near to cavity was performed to study the effect of the cavity on the dynamic behavior of the tunnel. In order to obtain the dynamic response of the tunnel embedded in a semi-infinite domain, a hybrid numerical technique was primarily developed. A dynamic fundamental solution in frequency domain for multi-layered half planes was derived and subsequently incorporated in the boundary element method. Coupling of the boundary element method for the far field with the finite element method for the near field is made by imposing compatibility condition of a displacement at the interface. The boundary element method is then coupled with the finite element method, which is utilized to model the near field including the tunnel and the cavity. In order to demonstrate the validity of the proposed technique, dynamic responses of single and multiply-layered semi-infinite structural systems are obtained by using the Kicker waveform and investigated in the limestone layer to find how the being and the location of the cavity affect the dynamic characteristics of the system.

• Fire Science and Engineering
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• v.33 no.6
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• pp.120-125
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• 2019

A real-scale combustion test was conducted on a vinyl flooring in a divided space, with 50 mL of an inflammable liquid sprayed on it. The combustion behavior of the vinyl flooring was studied in real time, and the carbonization patterns of the surface and cross-sections of the carbonized vinyl floor were analyzed. When the flame ignited by gasoline reached its peak, a continuously flaming region, intermittent flaming region, plume region, etc., were formed. The combustion of 50 mL gasoline on vinyl flooring took 26 s, and a halo pattern was observed. This test involved spraying kerosene evenly on the vinyl flooring and attempting to ignite the flooring using a gas torch, which failed. After the combustion of the vinyl flooring was complete, its carbonized range was measured to be 600 mm in length and 380 mm in width, and the carbonized area was 1000 ㎟. Heat transformed the coated layer of surface of the carbonized vinyl flooring into a carbonized layer, which became harder. The analysis of cross-section of the boundary surface of the carbonized vinyl flooring using a stereoscopic microscope showed that the vinyl flooring was bubbling, and that the white boundary layer at the bottom of the coated layer had disappeared.

• Steel and Composite Structures
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• v.33 no.2
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• pp.307-318
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• 2019

This is the first attempt to consider the nonlinear bending analysis of porous functionally graded (FG) thick annular and circular nanoplates resting on Kerr foundation. The size effects are captured based on modified couple stress theory (MCST). The material properties of the porous FG nanostructure are assumed to vary smoothly through the thickness according to a power law distribution of the volume fraction of the constituent materials. The elastic medium is modeled by Kerr elastic foundation which consists of two spring layers and one shear layer. The governing equations are extracted based on Hamilton's principle and two variables refined plate theory. Utilizing generalized differential quadrature method (GDQM), the nonlinear static behavior of the nanostructure is obtained under different boundary conditions. The effects of various parameters such as material length scale parameter, boundary conditions, and geometrical parameters of the nanoplate, elastic medium constants, porosity and FG index are shown on the nonlinear deflection of the annular and circular nanoplates. The results indicate that with increasing the material length scale parameter, the nonlinear deflection is decreased. In addition, the dimensionless nonlinear deflection of the porous annular nanoplate is diminished with the increase of porosity parameter. It is hoped that the present work may provide a benchmark in the study of nonlinear static behavior of porous nanoplates.

• Advances in nano research
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• v.15 no.6
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• pp.551-565
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• 2023

Coupled porous curved beams, due to their low weight and high flexibility, have many applications in engineering. This study investigates the vibration behavior of coupled porous curved beams in different boundary conditions. The system consists of two curved beams connected by a mid-layer of elastic springs. These beams are made of various materials, such as homogenous steel foam, and composite materials with PMMA (polymethyl methacrylate) and SWCNT (single-walled carbon nanotube) used as the matrix and nanofillers, respectively. To obtain equivalent material properties, the role of mixture (RoM) was employed, followed by the implementation of the porosity function. The system's governing equations were obtained by employing FSDT and Hamilton's law. To investigate thermal vibration, temperature was implemented as a load in the governing equations. The GDQ method was used to solve these equations. To demonstrate the applicability of the GDQ method in calculating the frequencies of the system and the correctness of the developed program, a validation study was conducted. After validation, numerous examples were presented to investigate the behavior of single and coupled curved beams in various material properties and boundary conditions. The results indicate that the frequencies of the curved beams and the system depend highly on the amount of porosity (n) and the distribution pattern. The system frequencies decreased with an increase in the porosity coefficient. The stiffness of the springs had no effect on the first mode frequency but increased frequencies of other modes in a specific range. The frequencies of the system decreased with an increase in environmental temperature.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1159-1160
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• 2006

For pure Molybdenum carburized in mixed gases of argon and carbon monoxide, microstructural observations were carried out. X-ray diffraction analysis for carburized specimens revealed that brittle ${\alpha}-Mo_2C$- layer hardly formed in the case of low carbon monoxide concentration. Fracture strength of the specimen carburized at 1673 K for 16 h is about 550 MPa higher than that of the un-carburized specimen. SEM observation revealed that with increasing carburizing temperature, the region demonstrating a transgranular fracture mode progressed towards the center of specimen. This result means that the grain boundaries were strengthened by the grain boundary diffusion of carbon and the strength of grain boundaries exceeded that of grain itself.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.25-30
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• 2001

The stress intensity factors for edge cracks located at the bonding interface between the semiconductor chip and the adhesive layer subjected to a uniform transverse tensile strain are investigated. Such cracks might be generated due to a stress singularity in the vicinity of the free surface. The boundary element method (BEM) is employed to investigate the behavior of interface stresses. The amplitude of complex stress intensity factor depends on the crack length, but it has a constant value at large crack lengths. The rapid propagation of interface crack is expected if the transverse tensile strain reaches a critical value.