• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.19 no.1
• /
• pp.1-15
• /
• 2007

In this study 8 nodes parallel linux cluster system is constructed and tested for the evaluation of computational efficiency and reliability of the Yellow Sea tidal hydrodynamics prior to compute storm surge inundation along the west coast of the Korean Peninsular. Computational efficiency increases up to 7 times based on NPB bench-marking test. Simulated results by pADCIRC on reproduction of the Yellow Sea tidal hydrodynamics resemble well with previous studies. According to model parameter tests, bottom friction coefficient, which should be appropriately represented shallow depth along the west coast, is essential factor in simulation.

• Structural Engineering and Mechanics
• /
• v.34 no.1
• /
• pp.61-84
• /
• 2010

Presented in this paper is the behaviour of asymmetric building isolated by the double variable frequency pendulum isolator (DVFPI). The DVFPI is an adoption of single variable frequency pendulum isolator (VFPI). The geometry and coefficient of friction of top and bottom sliding surfaces can be unequal. The governing equations of motion of the building-isolation system are derived and solved in incremental form. The analysis duly considers the interaction of frictional forces in the two principal directions developed at each sliding surface of the DVFPI. In order to investigate the behaviour of the base isolation using the DVFPI, the coupled lateral-torsional response is obtained under different parametric variations for a set of six far-fault earthquake ground motions and criterion to optimize its performance is proposed. Further, influences of the initial time period, coefficient of friction and frequency variation factors at the two sliding surfaces are investigated. The numerical results of the extensive parametric study help in understanding the torsional behaviour of the structure isolated with the double sliding surfaces as in the DVFPI. It is found that the performance of the DVFPI can be optimized by designing the top sliding surface initially softer and smoother relative to the bottom one.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.397-400
• /
• 2006

In this study, we experimentally investigate the possibility of skin-friction drag reduction by series of transverse cavities in a turbulent boundary layer flow. The effects of cavity depth (d), cavity length (l) and cavity spacing (s) on the skin friction drag are examined in the range of $Re_{\theta}\;=\;4030\;{\sim}\;7360$, $d/{\theta}_0\;=\;0.13\;{\sim}1.03$, l/d = 1 ~ 4 and s/d = 5 ~ 20. We perform experiments for twenty different cavity geometries and directly measure total drag force using in-house force measurement system. In most cases, the skin friction drag is increased. At several cases, however, small drag reduction is obtained. The variation of the skin ftiction drag is more sensitive to the cavity length than to the cavity depth or cavity spacing, and drag is reduced at $s/l\;{\geq}\;10$ and $l/{\theta}_0\;{\leq}\;0.26$ irrespective of the cavity depth. At $l/\bar{\theta}_0\;=\;0.13$ and s/l = 10, maximum 2% drag reduction is achieved. When the skin friction drag is reduced, there is little interaction between the flows inside and outside cavity, and the flow changed by the cavity is rapidly recovered at the following crest. A stable vortex is formed inside a cavity in the case of drag reduction. This vortex generates negative skin friction drag at the cavity bottom wall. Although there is form drag due to the cavity itself, total drag is reduced due to the negative skin friction drag.

• Journal of Biosystems Engineering
• /
• v.30 no.4 s.111
• /
• pp.229-234
• /
• 2005

Kinetic friction coefficient, bulk density, dynamic and static angle of repose, and terminal velocity of rice husk at the moisture range 7 to $23\%$ w.b. were determined. It could lead to better design and operation of the processing machinery and handling facilities. Friction coefficient was determined from the horizontal traction force measured by pulling the container holding a mass of rice husk on various plate materials. Dynamic angle of repose was calculated from the photos of bulk samples piled by gravity flow on a circular platform. Static angle of repose was determined by measuring the side angle of the bulk material which was left in a cylindrical container after natural discharge of the bulk sample through a circular hole in the bottom plate. Kinetic friction coefficients of rice husk were in the range of $0.254\~0.410,\;0.205\~0.520,\;0.229\~0.400,\;and 0.133\~0.420$ on PVC, mild steel, galvanized steel, and stainless steel, respectively. Bulk density, dynamic and static angle of repose, and terminal velocity were in the range of $91.7\~98.3$ $kg/m^3$, $40.2\~47.6^{\circ},\;52.8\~83.7^{\circ},$ and $1.36\~1.73$ m/s, respectively. These physical properties of rice husk increased linearly as the moisture content increased.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.12 no.6
• /
• pp.45-51
• /
• 2013

Friction stir welding using aluminum alloys has been widely applied for transportation vehicles because of the light specific weight, which can be used to obtain sound joint and high mechanical properties. This study shows the effects of rotation speed, welding speed, welding load, and tool shape on defect formation with extruded AA6005, which is used for railway vehicle structures of non-uniform thickness welded by friction stir welding using load control systems. Optical microscopy observations and liquid penetrant testing of each FSW joint were carried out in order to observe defect formation. Two kinds of defects, that of probe wear and that of lack of penetration in the bottom of the welded zone, were observed. In the case of using a taper shaped tool, the defect free zone is very narrow, within 100 kgf; however, in case of using a cylindrical shape tool, the defect free zone is wider.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.22 no.2
• /
• pp.73-78
• /
• 2010

Wave energy is dissipated mainly by friction on the seabed until the waves reach the surf zone. Many researchers have investigated the mechanism of wave friction and the bottom shear stress induced by wave motion at a certain point is now well estimated by introducing the wave friction factor related to the near bed velocity given by linear wave theory. The variation of wave energy or wave height over a long distance can be, however, estimated by an iteration process when the propagation of waves is strongly influenced by bed friction. In the present study simple semi-theoretical equation has been developed to compute the variation of wave height for the condition of wave propagation on a constant beach slope. The ratio of wave height is determined by the product of shoalng factor and wave height friction factor (frictional wave energy dissipation factor). The wave height estimated by the new equation is compared with the wave height estimated by the solution of numerical integration for the condition that the waves propagate on a constant slope.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.4C
• /
• pp.139-147
• /
• 2012

In this study, various laboratory tests using bottom ash, which has similar engineering properties with sand, were conducted in order to solve the problem of clogging in granular compaction pile and to address sand supply and demand. In particular, testing was performed to help reduce clogging and minimize voids in a crushed stone compaction pile constructed in soft ground. Based on compaction tests and large diameter direct shear tests, an optimum mixing ratio was determined to be 80:20 (crushed stone to bottom ash) because an 80:20 mixing ratio showed the highest shear strength. Test results showed that as the bottom ash content increased above 20%, internal friction angle decreased. Another test method showed freezing and thawing had little effect when the replacement ratio was over 40%. Therefore, bottom ash mixed compaction piles in soft ground are most economical at a 40% replacement ratio.

• Journal of Power System Engineering
• /
• v.13 no.2
• /
• pp.36-41
• /
• 2009

An experimental investigation was conducted to examine the fluid flow resistance in the rectangular channel with two inclined wire screen baffles. Two different types of wire screens; dutch weave and plain weave, were used as baffle devices in this experiment. Three kinds of baffles with different mesh specifications were made up of dutch type and four different kinds of baffles were made up of plain weave type. The stainless steel wire screen baffles were mounted on the bottom wall with varied angle inclination. Reynolds numbers were varied from 23,000 to 57,000. Results show that the mesh number of baffles plays an important role on friction factor behaviour. It is found that the baffle with the most number of meshes (type SA) has the highest fluid flow resistance.

• Journal of Mechanical Science and Technology
• /
• v.15 no.5
• /
• pp.639-645
• /
• 2001

Experimental investigations were conducted to study forced convection of fully developed turbulent flows in horizontal equilateral triangular ducts with different surface roughness pitch ratios (P/e) of 4, 8, and 16 on one side. The ducts bottom wall was heated uniformly and the other surfaces were thermally insulated. To understand heat transfer enhancement mechanism, heat transfer rates were measured. Smooth triangular ducts were also tested for benchmark purposes. The results were compared with previous results for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• 유체기계공업학회:학술대회논문집
• /
• 2006.08a
• /
• pp.179-183
• /
• 2006

Surface roughness is present in most of the microfluidic devices due to the microfabrication techniques. This paper presents lattice Boltzmann method (LBM) results for laminar flow in a microchannel with surface roughness. The surface roughness is modeled by an array of rectangular modules placed on top and bottom side of a parallel-plate channel. In this study, LBGK D2Q9 code in lattice Boltzmann Method is used to simulate flow field for low Reynolds number in a micro-channel. The effects of relative surface roughness, roughness distribution, roughness size and the results are presented in the form of the product of friction factor and Reynolds number. Finally, a significant increase in Poiseuille number is detected as the surface roughness is considered, while the effect of roughness on the microflow field depends on the surface roughness.