• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.141-143
• /
• 2006

It is well known that there are three mechanisms in the nozzle surface regression, namely ablation, mechanical erosion and chemical corrosion. There are Analogies among these three mechanisms. In order to compare the order of the magnitude of these mechanism, the analogy was adapted and the Mach number of the gas flow was expressed by the nozzle shape(location).

• Composites Research
• /
• v.14 no.3
• /
• pp.57-68
• /
• 2001

This paper predicted the thermal conductivity of spatially reinforced composites(SRC) by applying the volume averaging method and the thermal resistance method. The former method employs existing micro-mechanical theories and conventional transformation rules to obtain the constitutive relations for the unit cells of the composites and the latter one uses the analogy between the diffusion of heat and electrical charge. To verify the theoretical predictions, the thermal conductivity of 4-D(dimensional) SRC was examined experimentally. The comparison of the numerical results with those measured by the experiment showed good agreement.

• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.293-298
• /
• 2008

This paper attempts to quantify the effect of mismatch in creep properties on steady-state stress distributions for a welded branch vessel. A particular geometry for the branch vessel is chosen. The vessel is modeled by only two materials, the base and weld metal. Idealized power law creep laws with the same creep exponents are assumed for base and weld metals. A mismatch factor is introduced, as a function of the creep constant and exponent. Steady-state stress distributions within the weld metal, resulting from threedimensional, elastic-creep finite element (FE) analyses, are then characterized by the mismatch factor. We can find that average stresses in the weld can be characterized by the mis-match factor. And there is an analogy between elastic-creep and elastic-perfectly plastic.

• Proceedings of the KSME Conference
• /
• 2000.04b
• /
• pp.422-427
• /
• 2000

Propagation characteristics of tribrachial flames have been investigated experimentally in both two-dimensional and axisymmetric counterflows. Mixture fraction gradient at stoichiometric location is controlled by varying equivalence ratios at the two nozzles, one of which maintains rich while the other lean premixture. Tribrachial flames propagating through these mixtures are investigated. The propagation speed of tribrachial flames in two-dimensional counterflow decreases with fuel concentration gradient and has much higher speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed flame propagation, this excessively large propagation speed can be attributed to the tribrachial flame propagating with respect to burnt gas. Corresponding maximum speed in the limit of small mixture fraction gradient is estimated and extrapolated experimental results substantiate this limiting speed. As mixture fraction gradient approaches zero, a transition in propagation characteristics occurs, such that the propagation speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar behavior has been obtained for tribrachial flames propagating in axisymmetric counterflow.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.4
• /
• pp.69-75
• /
• 2017

In this study, the performances of five input split type hybrid electric vehicle sub-drivetrains were analyzed. The five sub-drivetrains consist of chain, helical gears and planetary gears. For the analyzing above five sub-drivetrains, the mathematical equations were derived. From the analysis, we found that the sub-drivetrain with chain shows slower acceleration performance and larger energy consumption on the city driving. And, the sub-drivetrain with only helical gear shows smallest energy consumption on the city driving. If the sub-drivetrain can change its gear speed, it shows fastest acceleration performance, but it has largest energy consumption on the city driving due to its additional auxiliary components.

• Journal of Ocean Engineering and Technology
• /
• v.18 no.1
• /
• pp.63-68
• /
• 2004

The purpose of this study is to estimate the contribution of concrete and shear reinforcement, in shear carrying capacity, on concrete beams, reinforced with steel and/or FRP rods. The experimental tests for 12 concrete beams, reinforced with steel and/or FRP rods, are carried out. Experimental parameters includes the mechanical properties of reinforcements in shear and bending, and the ratio of shear reinforcement. This study compares the experimental results of shear carrying capacity in concrete beams, reinforced with steel and/or FRP rods, with the proposed equations. According to the experimental results, the effect of the concrete in concrete beams reinforced with FRP rods is decreased with decreasing Young's modulus of longitudinal tensile reinforcement. This results from the large deflection of concrete beams reinforced with decreasing Young's modulus of longitudinal tensile reinforcement. Also, the contribution of shear reinforcement is smaller than the calculated value, using the truss analogy. This results from the fact that the stress redistribution is not exhibited after the break of shear reinforcement.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.12
• /
• pp.837-845
• /
• 2012

The purpose of this research is to investigate the heat transfer enhancement by the multiple tripping wires installed on a flat plate. Naphthalene sublimation technique is used to measure the local mass transfer coefficients, and then heat transfer coefficients are calculated using heat/mass transfer analogy. Experiments are performed for the developed and developing flow conditions. Local and average heat transfer coefficients from the flat plate with three tripping wires are compared with those of no and one tripping wire. Remarkable heat transfer enhancements are found resulting from the boundary layer separation by the tripping wires, especially in the laminar boundary layer.

• Journal of the Korean Society of Visualization
• /
• v.20 no.3
• /
• pp.27-35
• /
• 2022

A problem on the sloshing flow of highly-viscous fluid in a rectangular box was revisited by both of theoretical approach and experimental visualization method. Based on the theoretical prediction that a linear shape of free surface is prevailing in bulk zone, it has been studied an analogy between a near wall coating flow in sloshing problem and dip coating flow in Landau-Levich problem. Phenomenological observation confirms that, in the case of highly-viscous fluid, I.e., R_e ≪ 1, viscous dominant near-wall flow in sloshing problem is identical to dip coating flow generated by drag-out of the plate being in both motion of vertical translation and horizontal rotation.

• Journal of computational fluids engineering
• /
• v.17 no.4
• /
• pp.81-86
• /
• 2012

The objective of the present study is to investigate the effects of various turbulence models on the aerodynamic noise of an air-conditioner (AC) indoor unit. The results from URANS (unsteady Reynolds-averaged Navier-Stokes) simulations with the standard k-$\varepsilon$, k-$\omega$ shear stress transport (SST) and Spalart-Allmaras (S-A) turbulence models were analyzed and compared with the noise data from the experiments. The frequency spectra of the far-field acoustic pressure were computed using the Farrasat equation derived from the Ffowcs Williams-Hawkings (FW-H) equation based on the acoustic analogy model. Two fixed fan casings and the rotating cross-flow fan were used as the source surfaces of the dipole noise in the Farrasat equation. The result with the standard k-$\epsilon$ model showed a much better agreement with the experimental data compared to the k-w SST and S-A models. The differences in the pressure spectra from the different turbulence models were discussed based on the instantaneous vorticity fields. It was found that the over-estimated power spectra with the k-w SST and S-A models are related to the emphasized small-scale vortices produced with these models.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.3
• /
• pp.269-274
• /
• 2014

In this study, low noise designs for a Savonius wind turbine were numerically investigated. As was reported in our previous study, the harmonic components with a fundamental frequency higher than the BPF were identified as being dominant in the noise spectrum of a Savonius wind turbine, and these components were a result of vortex shedding. On a basis of this observation, an S-shaped blade tip is proposed as a means of reducing the noise generated by small vertical(Savonius) wind turbines. This blade induces phase differences in the shedding vortices from the blades, and thus reduces the noise from the wind turbine. The aerodynamic noise characteristics of the conventional and "S-shaped" Savonius turbines were investigated by using the Hybrid CAA method where the flow field around the turbine is computed using the CFD techniques and the radiated noise are predicted by applying acoustic analogy to the computed flow field data. The degree of noise reduction resulting from the proposed design and its reduction mechanism were confirmed by comparing the predicted noise spectrum of these turbines and the flow characteristics around them.