• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1119-1127
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• 2000

Convective heat transfer in a channel filled with porous media has been analyzed in this paper. The two-equation model is applied for the heat transfer analysis with the velocity profile, considering both the inertia and viscous effects. Based on a theoretical solution, the effect of the velocity profile on the convective heat transfer is investigated in detail. The Nusselt number is obtained in terms of the relevant physical parameters, such as the Biot number for the internal heat exchange, the ratio of effective conductivities between the fluid and solid phases, and hydraulic boundary layer thickness. The results indicate that the influence of the velocity profile is characterized within two regimes according to the two parameters, the Biot number and the conductivity ratio between the phases. The decrease in the heat transfer due to the hydraulic boundary layer thickness is 15% at most within a practical range of the pertinent parameters.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.5
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• pp.90-99
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• 1995

A numerical method is proposed to synthesize automotive cam profiles. An arbitrary acceleration profile for the cam follower motion is divided into several segments, each of them is described by a Hermite curve. A cam profile is defined by control point locations and control variables assigned to each segment. Closed form equations are derived for velocity and displacement constraints which should be satisfied for the curve to be a cam profile. Because the method is flexible and provide arbitrary local controllability, any types of cam acceleration profile can be reproduced by the method. The method is expecially useful for the design of roller type OHC valve trains which need precise local control in the cam profile design to avoid under-cutting problems.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.135-146
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• 2003

Uphole test is a seismic field test using receivers on ground surface and a source in depth. In this paper, the uphole test using SPT(standard penetration test) which is economical and reliable for obtaining shear wave velocity profile was introduced. In the proposed uphole test, SPT sampler which is common in site investigation, was used as a source and several 1Hz geophones in line were used as receivers. Test procedures in field and interpretation methods for obtaining interval times and for determining shear wave velocity profile considering refracted ray path were introduced. Finally, uphole test was performed at three sites, and the applicability of the proposed uphole test was verified by comparing wave velocity profiles determined by the uphole test with the profiles determined by downhole test, SASW test and SPT-N values.

• New & Renewable Energy
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• v.5 no.4
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• pp.21-27
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• 2009

Potential yield of micro wind turbine on the roof of urban high rise buildings is estimated. Urban wind profile is modeled as logarithmic profile above the mean building height with roughness length 0.8, displacement 7.5 m. Mean wind velocity from the meteorological agency data at the hight of 50m is used. Wind velocity changes are simulated on the rectangular roof of 26, 45, 53 degree pitch and the circular roof by computational fluid dynamics and RNG k-$\varepsilon$ turbulence models. Wind velocity increased approximately by a factor of the order of 270 % on the 26 degree pitched roof. In the 100 m and 200 m high buildings, wind enhancement is greater at the front side than at the center of the building. In the building arrangement model wind velocity changes abruptly and it becomes wind gusts. When commercial wind turbines are installed on the building roof, average power and annual power generation enhanced by 3~4 times than normal wind velocity at 50m and 6 kw wind turbine can generate 1053 kwh per month on the 26 degree pitched roof at 50m height and sufficiently supply electrical power with 15 household for common electrical use and food waste disposer. However, power output will vary significantly by the wind conditions in the order of $\pm$ 20 %.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.661-669
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• 1997

This paper presents a theoretical analysis for a velocity profile of fluid-granule mixed flow and a sheet erosion of an embankment having noncohesive materials due to overflow. The velocity profile were obtained using the stress-strain relationships based on a grain-inertia regime and an erosion depth was obtained using dynamic Coulomb criterion. Experiments were performed to compare with theoretical values and fairly good agreements were found. Theoretical results on velocity profiles, which can be applied to any type of velocity profiles in a fluid-granule mixed flow, showed a considerable improvement for the existing theories on a debris flow. for a design purpose, formulas and figure diagrams for obtaining a velocity profile, an erosion depth, an overflow depth and a granular discharge were proposed for given values of a flood discharge, particle properties and embankment scale.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.55-63
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• 2012

The evaluation of shear modulus (or shear wave velocity) profile of the site is very important in various fields of geotechnical engineering and various surface wave methods have applied to determine the shear wave velocity profiles and showed good performance. Surface wave methods evaluate the dispersion curve in the field and determine the shear wave velocity profile through the inversion process. In this paper, the automated inversion process using the genetic algorithm is developed for HWAW method which is one of surface wave methods recently developed. The proposed method uses the error function based on the wavelength domain dispersion curve and can determine the reliable shear wave velocity profile not only in shallow depth but also in deep depth. To estimate the validity of the proposed method, numerical simulations and field test were performed and the proposed method was applied to determine the shear wave velocity profiles. Through the numerical simulations and field applications, the promising potential of the proposed method was verified.

• The KSFM Journal of Fluid Machinery
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• v.9 no.6 s.39
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• pp.17-21
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• 2006

The numerical simulations on the train entering a tunnel were performed by solving unsteady axi-symmetric problems. In the case that 5th order velocity profile is used to reduce the effects of the pressure wave generated by the train starting abruptly, the effect of the initial distance between the train and the tunnel were examined. The impulsive start gives undesired pressure disturbances to the flow field including inside the tunnel. But 5th order velocity profile with initial distance more than 80 m gives much stable pressure variance in time, and pressure distribution inside the tunnel in space. The distance to the train reaches the highest running velocity from the start should be more than 80 m when the train speed is 350 km/h.

• The KSFM Journal of Fluid Machinery
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• v.14 no.6
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• pp.76-84
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• 2011

The effect of inlet velocity profile on the heat transfer coefficient in a rotating smooth channel was investigated experimentally. Three simulated inlet flow conditions of fully developed, uniform, and distorted inlet conditions were tested. The Reynolds number based on the channel hydraulic diameter was ranged from 10,000 to 30,000 and the transient liquid crystal technique was used to measure the distribution of the heat transfer coefficient in the rotating channel. Results showed that the overall heat transfer coefficient increased as the Reynolds number increased. Also, the distribution of the heat transfer coefficient was strongly affected by the inlet flow condition. Generally, the fully developed flow simulated condition showed the highest heat transfer coefficient.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.389-390
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• 2006

The cycloidal reducer is one of the velocity controlling equipments in machinery. It has advantages of the higher reduction ratio, the higher accuracy, the easier adjustment of the transmission ratio and the smaller workspace than any other kinds of the reducers. This paper proposes a simple and exact approach for the lobe profile design of the two teeth difference cycloidal plate gear, which is different from the standard cycloidal reducer, by means of the principle of the instant velocity center in the general contact mechanism and the homogeneous coordinate transformation.

• Proceedings of the KIEE Conference
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• 2004.10a
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• pp.98-100
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• 2004

This paper is proposed vibration minimize method of PMLSM which is designed to minimize detent force. To minimize of vibration at acceleration discontinuous point of velocity curve, genetic algorithm is applied. The vibration characteristic is compared general trapezoid velocity curve with proposed velocity profile.