• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.5
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• pp.437-446
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• 2011

Performance of array sonars towed underwater is limited due to the self-noise induced mainly by the strumming vibration of the towing cable and also turbulent flow around the acoustic sensor module. The vibration of the towing cable generates axisymmetric waves that propagate along the acoustic module of the array sonar and produce self-noise. The present study aims to investigate the characteristics of the self-noise induced by the axisymmetric vibrations of the acoustic module. The waves of interest are the bulge and extensional waves propagating along the fluid-filled elastic hose. Dispersion relations of these waves are predicted by means of the numerical simulation to evaluate the wave speeds. The self-noise induced by the axisymmetric waves are formulated taking into account the damping of the elastic hose and the effect of the damping is investigated.

• Transactions on Electrical and Electronic Materials
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• v.11 no.2
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• pp.65-68
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• 2010

The operation principle of a traveling wave rotary type ultrasonic motor can be successfully applied to the fluidic transfer mechanism of the micro-pump. This paper proposes an innovative valveless micro-pump type that uses an extensional vibration mode of a traveling wave as a volume transportation means. The proposed pump consists of coaxial cylindrical shells that join the piezoelectric ceramic ring and metal body, respectively. In order to confirm the actuation mechanism of the proposed pump model, a numerical simulation analysis was implemented. In accordance with the variations in the exciting wave mode and pump body dimension, we analyzed the vibration displacement characteristics of the proposed model, determined the optimal design condition, fabricated the prototype pump from the analysis results and evaluated its performance. The maximum flow rate was approximately $595\;{\mu}L/min$ and the highest back pressure was 0.88 kPa at an input voltage of $130\;V_{rms}$. We confirmed that the peristaltic motion of the piezoelectric actuator was effectively applied to the fluid transfer mechanism of the valveless type micro pump throughout this research.

• Korea-Australia Rheology Journal
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• v.19 no.3
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• pp.147-156
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• 2007

The orientation and deformation of polymer chains in a confined channel flow has been investigated. The polymer chain was modeled as a Finitely Extensible Nonlinear Elastic (FENE) dumbbell. The Brownian configuration field method was extended to take the interaction between the flow and local chain dynamics into account. Drag and Brownian forces were treated as anisotropic in order to reflect the influence of the wall in the confined flow. Both Poiseuille flow and 4 : 1 contraction flow were considered. Of particular interest was molecular tumbling of polymer chains near the wall. It was strongly influenced by anisotropic drag and high shear close to the wall. We discussed the mechanism of this particular behavior in terms of the governing forces. The dumbbell configuration was determined not only by the wall interaction but also by the flow type of the geometric origin. The effect of extensional flow on dumbbell configuration was also discussed by comparing with the Poiseuille flow.

• Korea-Australia Rheology Journal
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• v.11 no.3
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• pp.225-232
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• 1999

This study presents 1-dimensional simple model for sheet casting or rectangular fiber spinning process. In order to achieve this goal, we introduce the concept of force flux balance at the die exit, which assigns for the extensional flow outside the die the initial condition containing the information of shear flow history inside the die. With the Leonov constitutive equation that predicts non-vanishing second normal stress difference in shear flow, we are able to describe the anisotropic swelling behavior of the extrudate at least qualitatively. In other words, the negative value of the second normal stress difference causes thickness swelling much higher than width of extrudate. This result implies the importance of choosing the rheological model in the analysis of polymer processing operations, since the constitutive equation with the vanishing second normal stress difference is shown to exhibit the characteristic of isotropic swelling, that is, the thickness swell ratio always equal to the ratio in width direction.

• 한국가시화정보학회:학술대회논문집
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• 2006.12a
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• pp.96-101
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• 2006

3-D visualization using confocal laser scanning microscopy (CLSM) in a chaotic micromixer was performed as a reproduction experiment and the feasibility of 3-0 imaging technique in the microscale was confirmed. For diagonal micromixer (DM) and two types of staggered herringbone micromixers (SHM) designed by Whitesides et al., to verify the evolution of mixing, cross sectional images are reconstructed at the end of every cycle. In a DM, clockwise rotational flow motion generated by diagonal ridges placed on the floor of micromixer is observed and this motion makes the fluid commingle. On the contrary, there are two rotational flow structures in the SHM and the centers of rotation exchange their position each other every half cycle because of the V shape of ridges varying their orientation every half cycle. Local rotational flow and local extensional flow generated by the complicate ridge pattern make the flow be chaotic and accelerate the mixing of fluid. The dominant parameter that influences on the mixing characteristic of SHM is not the length of micromixer but the number of ridges under the same flow configurations.

• Economic and Environmental Geology
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• v.49 no.4
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• pp.315-323
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• 2016

This study reports a gneiss dome in the Hongseong area, southwestern margin of the Gyeonggi massif. This gneiss dome, named here as 'Oseosan dome' because it is located around the Oseosan, the highest peak along the western coastal area, is composed mainly of the Neoproterozoic to Paleozoic ortho- and paragneiss, mafic metavolcanic rock, and metadolerite. Migmatization affected these rock units, in which leucocratic(granitic) materials derived from anatexis frequently occur as patch and vein parallel to or cutting through internal foliation. The Oseosan dome shows overall concentric geometry and outward-dipping internal foliation, but also partly complicatedly changeable or inward-dipping foliation. Taking available petrological and geochronological data into account, the Oseosan dome is interpreted to be exhumed quickly into the upper crustal level during the Late Triassic, accompanied in part with anatexis and granite intrusion. In addition, extensional shear zone intruded by the Late Triassic synkinematic granite and sedimentary basin have been reported around the Oseosan dome. These evidences possibly suggest that the Oseosan dome formed in closely associated with the Late Triassic extensional movement and diapiric flow. Alternatively, 1) thrust- or reverse fault-related doming or 2) interference between independent folds during structural inversion of the Late Traissic to Middle Jurassic sedimentary basin can be also considered as dome-forming process. However, considering the northern limb of the Oseosan dome, cutting by the Late Traissic granite, and the southern limb, cutting by contractional fault reactivated after the Middle Jurassic, it is likely that the domal structure formed during or prior to the Late Triassic.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.269-280
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• 2009

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.

• Korea-Australia Rheology Journal
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• v.16 no.3
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• pp.117-128
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• 2004

The effect of molecular parameters on the steady vortex behaviors in the inertial viscoelastic flow past a cylinder has been investigated. FENE-CR model was considered as a constitutive equation. A recently developed iterative solution method (Kim et al., (in press)) was found to be successfully applicable to the computation of inertial viscoelastic flows. The high-resolution computations were carried out to understand the detailed flow behaviors based on the efficient iterative solution method armed with ILU(0) type pre-conditioner and BiCGSTAB method. The discrete elastic viscous split stress-G/streamline upwind Petrov Galerkin (DEVSS-G/SUPG) formulation was adopted as a stabilization method. The vortex size decreased as elasticity increases. However, the vortex enhancement was also observed in the case of large extensibility, which means that the vortex behavior is strongly dependent upon the material parameters. The longitudinal gradient of normal stress was found to retard the formation of vortex, whereas the extensional viscosity played a role in the vortex enhancement. The present results are expected to be helpful for understanding the inertial vortex dynamics of viscoelastic fluids in the flow past a confined cylinder.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2342-2354
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• 2002

The present study has numerically predicted both the flow -induced and thermally-induced residual stresses and birefringence in injection o. injection/compression molded center -gated disks. Analysis system for entire molding process was developed based on an ap propriate physical modeling including a nonlinear viscoelastic fluid model, stress-optical law, a linear viscoelastic solid model, free volume theory for density relaxation phenomena and a photoviscoelasticity and so on. Part I presents physical modeling a nd typical numerical analysis results of residual stresses and birefringence in the injection molded center-gated disk. Thermal residual stress was found to be extensional near the center, compressive near the surface and tend to become toward tensional at the surface. A double-hump profile was obtained across the thickness in birefringence distribution: nonzero birefringence is found to be thermally induced, the outer peak is due to the shear flow and subsequent stress relaxation during the filling stage a nd the inner peak is due to the additional shear flow and stress relaxation during the packing stage. Predicted birefringence including both the flow -induced and thermally-induced one becomes quite similar to the experimental one.

• Korea-Australia Rheology Journal
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• v.13 no.1
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• pp.1-12
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• 2001

This paper describes the application of our recently developed two-phase model for flow-induced crystallization (FIC) to the simulation of fiber spinning and film blowing. 1-D and 2-D simulations of fiber spinning include the combined effects of (FIC), viscoelasticity, filament cooling, air drag, inertia, surface tension and gravity and the process dynamics are modeled from the spinneret to the take-up roll device (below the freeze point). 1-D model fits and predictions are in very good quantitative agreement with high- and low-speed spinline data for both nylon and PET systems. Necking and the associated extensional softening are also predicted. Consistent with experimental observations, the 2-D model also predicts a skin-core structure at low and intermediate spin speeds, with the stress, chain extension and crystallinity being highest at the surface. Film blowing is simulated using a "quasi-cylindrical" approximation for the momentum equations, and simulations include the combined effects of flow-induced crystallization, viscoelasticity, and bubble cooling. The effects of inflation pressure, melt extrusion temperature and take-up ratio on the bubble shape are predicted to be in agreement with experimental observations, and the location of the frost line is predicted naturally as a consequence of flow-induced crystallization. An important feature of our FIC model is the ability to predict stresses at the freeze point in fiber spinning and the frost line in film blowing, both of which are related to the physical and mechanical properties of the final product.l product.