• Macromolecular Research
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• 제17권10호
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• pp.807-812
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• 2009

In this work, we focus on the tumbling dynamics of rod-like and semi-flexible polymers in mixed flows, which vary from simple shear to pure rotation. By employing a bead-rod model, the tumbling pathways and periods are examined with a focus on the angular distribution of their orientation. Under the mixed flows, the tumbling dynamics agreed well with earlier studies and confirmed the predicted scaling laws. We found that the angular distribution deviates from that of shear flow as the flow type approaches pure rotation. Finally, we investigated the angular distribution of $\lambda$-DNA in a shear flow and found that the present numerical simulations were in quantitative agreement with the previous experimental data.

• 한국자동차공학회논문집
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• 제5권2호
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• pp.149-161
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• 1997

Masked intake ports of a DOHC gasoline engine were divised and the shape was optimized to maximize the swirling and tumbling motions in the cylinder. Performances of the ports, swirling number, tumbling number and discharge coefficient were measured by Ricardo's rig test. By combination of the angle and height of the protrusions in the intake ports wall, swirling and tumbling strength can be controlled and the port shape can be optimized to increase the swirling number 13 times and tumbling number 2 times larger than those of an original port of DOHC engine with the expense of 3% decrease of discharge coefficient.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.353-356
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• 2004

When a body falls in fluid, the body often experiences autorotations, namely, various kind of rotating motions, such as tumbling, flat spin and coming. Tumbling is a rotating motion with an axis perpendicular to a falling direction. Tumbling is a very important phenomenon in aeronautical and space engineering, ballistics and meteorology. For example, when an satellite re-en-tries into the atomosphere, its body collapses into many fragments which are disperse in the wide range of field. Some fragments fall in tumbling motion. Then tumbling is useful to predict fragment's motion.(omitted)

• 산업기술연구
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• 제19권
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• pp.51-57
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• 1999

This research has an object to find out how the position of inlet valve influence swirling and tumbling of turbulence inside the combustion chamber of 4 valve engine. The computational analysis of three dimensional complicated turbulence flow in the cylinder is done by the KIVA-3V program to carry out this object. One use 6 valve positions with the bowl type of piston cavity. The swirl ration and the tumbling ratio of flow filed are evaluated quantitatively to find out how each valve position influence flow phenomena in the combustion chamber during the intake and compression processes.

• 한국자동차공학회논문집
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• 제13권4호
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• pp.49-57
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• 2005

In this study, in-cylinder flow of the swirl chamber type diesel engine numerically simulated by VECTIS code. The flow fields during the intake and compression process were also investigated in detail. Numerical results revealed that the generation and distortion of the swirling, tumbling vortices and those influences on turbulence kinetic energy by shape of the jet passage, angle and area. It was also found that flow characteristics were affected by inflow velocity that depends on change of the jet passage shape. Swirl ratio was increased according to decrease of jet passage area, and was affected by piston motion according to increase of jet passage angle. Tumbling vortices had the similar in various cases, but tumble ratio was increased with the inflow velocity. The generation of turbulence kinetic energy was considerably influenced by complex effects of swirling and tumbling vortices.

• 한국세라믹학회지
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• 제20권2호
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• pp.166-172
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• 1983

In this study the sillicon-alloyed isotropic pyrolytic carbon was deposited in the tumbling bed from the pyrolysis of propane and silicon tetrachloride and investigated whether the silicon-alloyed isotropic pyrolytic carbon deposited in this study was usable as bionaterial or not. The silicon-allyed isotropic pyrolytic carbon was varied by controlling the process variables such as propane con-concentration and the argon flow rate flowing in to the silicon tetrachloride bubbler at a fixed reaction bed tempera-ture of 120$0^{\circ}C$ a rotation of reaction tube of 40 rpm a bed particle weight of 7.5 g and a total flow rate of 21/min; the propane concentration was varied from 10 to 70 and the argon flow rate flowing into the silicon tetrachloride bubble from 0 to 1000 cc/min. The results show that the silicon-alloyed isotropic pyrolytic carbon was obtained at all conditions investigated, . And then the alloyed silicon content is rangion from 7 to 14.5 wt%. The density and deposition rate of deposited silicon-alloyed isotropic carbon increased axxording to silicon content and propane concentration. And the apparent crystal-size(Lc) of pyrolytic carbon is not changed with silicon content. The density and apparant crystallite size are respec-tively in the range of 1.94 to 2.06 and 20 to 25$\AA$ It is shown that the silicon-alloyed isotropic pyrolytic carbon ob-tained in this experiment is usable as biomaterial.

• Korea-Australia Rheology Journal
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• 제19권3호
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.934-939
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• 2001

In computational study of the flow in piston engines and the flow through moving valves, the use of moving vertices is essential for modelling flows with moving boundaries. The positions of cell vertices in such cases must be allowed to vary with time. To simulate 3-dimensional port-valve and piston-cylinder of HIMSEN 6H21/32 engine, a commercially available code, STAR-CD, was used. Changes in mesh geometry was specified by PROSTAR commands.(i.e. the Change Grid operation in the EVENTS command module.) Control of the intake flow is expected to play an important role as designers seek to obtain better fuel spray characteristics, fuel mixing and mixture preparation, combustion performance, and emissions reductions to meet national standards. As a result of analysis, velocity fields indicate the presence of a structured flow comprised of one pair of counter-rotating vortices under the intake valve during the early induction process. These flow structures remain visible for most of the intake process. As the piston moves towards BDC, these vortices develops into a larger tumbling motion that dominates the flow structure.

• 한국전산유체공학회지
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• 제17권2호
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• pp.107-112
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• 2012

We explored the dynamic motions and the lateral equilibrium positions of an elastic capsule in channel flow at moderate Reynolds number varying Re, aspect ratio, size ratio, membrane stretching and bending coefficient. The transition of tank-treading/swinging to tumbling motion was observed in the simulations and the transition of dynamic motions for capsules resulted in different trend of the variation in the lateral equilibrium positions. Though other conditions were similar, the capsule with tumbling motion migrated closer to the wall than that with tank-treading motion.

• 한국자동차공학회논문집
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• 제7권7호
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• pp.1-14
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• 1999

In the present study, the flame factor which primarily influence the simulation accuracy of the combustion process in a gasoline engine was modeled as a nonlinear function of turbulent intensity to laminar flame speed ratio. Multi-length-scale production rate model for turbulent kinetic energy equation was introduced to consider the different length scales of the swirling and tumbling motions in cylinder on the production rte of turbulent kinetic energy. By7 introducing the multi-length-scale production rate model for the turbulent kinetic energy equation, the predictions of turbulent burning velocity , cylinder pressure, mass burning rate and engine performance of a gasoline engine can much be improved.