• 한국전산유체공학회:학술대회논문집
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• 1996.05a
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• pp.105-110
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• 1996

In the present paper, flow fields around two dimensional single and two circular cylinders are analysed by a finite difference method. Navier-Stokes and the continuity equations an solved to simulate the flow fields. A overlapped grid system(the composite of a body boundary-fitted grid system near the body and a rectangular grid system for other flow fields) is used for this calculation. In the use of overlapped grid system, it is most significant thing to exchange the physical quantities from one grid system to the other one continuously, In this research, the linear interpolations of physical quantaties are done for this purpose in the overlapped region. The numerical calculations are carried out for the flows around a circular cylinder and two cylinders to verify the accuracy of present method. The flow fields around two cylinders facing the flow with side by side and tandem arrangement are analysed. The results are compared to other experimental and computational ones done in other single grid system.

• KSTLE International Journal
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• v.5 no.1
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• pp.14-22
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• 2004

The sub-surface stress field beneath the gear's contact surface caused by the surface pressure in lubricated condition is analyzed. To evaluate the influence of the clearances between a gear tooth and a pinion tooth on the stress field, two kinds of tooth profile models - conventional cylinder contact model and new numerical model - were chosen. Kinematics of the gear is taken into account to obtain the numerical model which is the accurate geometric clearances between a gear tooth and a pinion tooth. Transient elasto-hydrodynamic lubrication (EHL) analysis is performed to get the surface pressure. The sub-stress field is obtained by using Love's rectangular patch solution. The analysis results show that the sub-surface stress is quite dependent on both the surface pressures and the profile models. The maximum effective stress of the new model is lower than that of the old model. The depth where the maximum effective stress occurs in the new model is not proportional to the intensity of the external load.

• Bulletin of the Society of Naval Architects of Korea
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• v.23 no.2
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• pp.27-32
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• 1986

This paper describes an application of the adaptive finite element computations to a free surface flow problem in a canal. A-posteriori error estimates for the adaptive finite element computations are based on the dual extremum principles. Previously the dual extremum principles were applied to compute the upper and lower bounds of the added mass of two-dimensional cylinders in a canal[1,2]. However, the present method improves the convergence of the computed results by utilizing the local error estimates and by applying the adaptive meshes in the finite element computations. In a test result using triangular elements it is shown that the numerical error in the adaptive finite elements reduces quadratically compared with that in a uniform mesh subdivision.

• Progress in Superconductivity and Cryogenics
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• v.20 no.2
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• pp.29-33
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• 2018

Although high-temperature superconducting (HTS) magnets have the potential merit of producing ultra-high field (>25 T), they have been not easy to apply to Nuclear Magnetic Resonance (NMR) because of the difficulty of field homogeneity improvement. This paper presents a design technique of passive shimming for HTS magnets. Ferromagnetic shimming design code was developed though MALAB, which includes the optimization algorithm. The proper shim element size was determined by a simulation. This design technique was verified by a case study design of a 3-T HTS magnet. We succeed to improve field homogeneity of the magnet from 634 ppm to 6.39 ppm at 10-mm diameter sphere volume. Feasibility of passive shimming for all-HTS NMR magnet was confirmed by this result.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.70-75
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• 2004

The shearing process for the sheet metal is normally used in the precision elements such as a lead frame of IC chips. In these precision elements, the burr formation brings a bad effect on the system assembly and demands the additional deburring process. In this paper, we developed the small size precision punching system to investigate burr formation mechanism and to present kinematically punch-die aligning methodology between the rectangular shaped punch and die. The punch is driven by an air cylinder and the sheet metal is moving on the X-Y table system which is driven by two stepping motors. The whole system is controlled by microprocessor and is communicated with each other by RS232C serial communication protocol. Punching results are measured manually using the SEM photographs and are compared aligning result with miss aligning one.

• Journal of the Korean Wood Science and Technology
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• v.40 no.1
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• pp.26-37
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• 2012

Recently, the demand and supply on the Hanok have been increased. However, Hanok should be requested larger section of structural members because of excessive roof weight. So, structural skin-timber was manufactured to get a lightweight structural member. The structural skin-timber has exterior shape with larger section but a great volume of wood be removed. The reduced strength of structural skin-timber can be supplemented by hybridizaion of structural member. Japanese larch and Domestic pine were used to manufacture the structural skin-timber. Structural skin-timbers of rectangular shape and cylinder shape were manufactured and tested to evaluate the bending properties. The intended strength property could not be obtained because member had been suffered severe damage by precision deficiency of manufacturing machine. However, if precision of manufacturing machine would be improved and additional hybridizaion of structural skin-timber would be done, lightweight structural member will be able to be manufactured. Structural skin-timber did not showed statistical significancy between two species, so it is possible to use pine mixed with larch. Only MOR of larch showed statistical significancy between rectangular shape and cylinder shape, so it is necessary to use of those as separate things. However, the rest of skin-timber can be judged mixed using because of non statistical significancy. The objective of this study was the development of lightweight larger structural member with relatively strength. If hybrid member of skin-timber could be developed with wood-ceramics, lightweight steel and more, it can be possible to be used as a building material of Hanok, interior material, post & beam construction material and more.

• Journal of Biosystems Engineering
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• v.34 no.6
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• pp.404-410
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• 2009

This study was carried out to develop a self-propelled type explosive subsoiler for improving the root zone soil conditions in orchard and other forest fields. Prototype was designed to be able to inject air and other soil improving material such as lime into soil at the same time, and thus improve the air permeability and drainage of orchard soils to promote the root growth of tree for high quality fruit production. Soil penetration device of explosive subsoiler is composed of air hammer, penetration rob and air injection nozzle. To support the soil penetration device of explosive subsoiler to penetrate vertically, modified Scott-Russel mechanism was used. Timing control device for simultaneous injection of soil improving material with air was attached to the out side wall of air cylinder and as the cylinder move, the soil improving material was injected into soil at the same time. Turning radius of prototype was 2.2-2.3 m with good mobility in sloped land. It took approximately 1 minute for lime injection system to reach the optimum pressure of 9.9 kg/$cm^2$, average 10-20 seconds were required to rupture soil with the depth of 50 cm and 2-3 seconds were required for explosion, so all in all about 1 minute and 20 seconds were required for one cycle of explosion. Maximum soil rupture depth and diameter were 50 cm and 3-4 m respectively depending on the soil type and soil moisture content. For final design of explosive subsoiler inclination angle of lime hopper was increased from 60 degree to 70 degree and the shape of hopper was changed from rectangular cone to circular cone to solve the clogging problem of lime at out let. Agitating system operated by compressed air was attached to the metering device of the prototype, thus more than 90 cc of lime was discharged per cycle from metering device without clogging problems.

• Journal of the Korean Society of Safety
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• v.26 no.2
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• pp.32-35
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• 2011

Experimental studies were carried out in an explosion chamber to investigate the influences of multiple cylinder obstacles on local flame propagation. The chamber dimension is 235 mm in height with a $1,000{\times}950\;mm^2$ rectangular cross section and a large vent area of $1,000{\times}320\;mm^2$. Multiple cylinder bars with obstruction ratio of 30% were used. In order to examine the interaction between the propagating flames and the obstacles, temporally resolved flame front images were recorded by a high speed video camera. The propagation behaviour of local flame fronts around the left obstacle was analyzed in terms of two different methods such as the incremental burnt area divided by the flame front length and the average of the local propagation velocity determined at each point along the flame front. It was found that two methods give good consistency.

• Radiation Oncology Journal
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• v.18 no.4
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• pp.337-344
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• 2000

Purpose :To design and test test CT simulator phantom for geometrical test. Materials and Methods : The PMMA phantom was designed as a cylinder which is 20 cm in diameter and 24 cm in length, along with a 25$\times25\times31cm^{3}$ rectangular parallelepiped. Radio-opaque wires of which diameter is 0.8 mm are attached on the other surface of the phantom as a spiral. The rectangular phantom was made of four 24$\times24\times0.5 cm^{3}$ square plates and each plate had a 24$\times24 cm^{2}$, 12$\times12cm^{2}$, 6$\times6 cm$^{2}$ square line. The squares were placed to face the cylinder at angles 0 $^{\circ}$ , 15 $^{\circ}$ , 30 $^{\circ}$ ,respectively. The rectangular phantom made it possible to measure the field size, couch angle, the collimator angle, the isocenter shift and the SSD, the measurements of the gantry angle from the cylindrical part. A virtual simulation software, AcOSim, offered various conditions to perform virtual simulations and these results were used to perform the geometrical Quality assurance of CT simulator. Results : A 0.3$\~$0.5 mm difference was found on the 24 cm field size which was created with the DRR measurements obtained by scanning of the rectangular phantom. The isocenter shift, the collimator rotation, the couch rotation, and the gantry rotation test showed 0.5$\~$1 mm, 0.5$\~$l$^{\circ}$ 0.5$\~$ 1$^{\circ}$ , and 0.5-1 $^{\circ}$ differences, respectively. We could not find any significant differences between the results from the two scanning methods. Conclusion :The geometrical test phantom developed in the study showed less than 1 mm (or 1 $^{\circ}$ ) differences. The phantom could be used as a routine geometrical QC/QA tools, since the differences are within clinically acceptable ranges.

• The Korean Journal of Malacology
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• v.24 no.2
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• pp.131-136
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• 2008

Growth and survival of the spat of arkshell, Scapharca broughtonii were investigated for the improvement of survival in intermediate culture with different shape of protective net and type of preventive net of spat loss. The growth performance of the spat of arkshell was observed for 60 days by using different forms of protective net, as the exposure form with an average shell length of $12.8{\pm}3.2$ mm(P<0.05), the fish pot form with $12.2{\pm}3.5$ mm, the cylinder form with $11.9{\pm}3.8$ mm and the last one is the rectangular form with $10.9{\pm}3.7$ mm. Their numerical value did not show any marked difference with each other. But in case of survival rate, the fish pot form showed highest survival rate which is 43.7% and the significantly lowest was showed by the exposure form, which is 5.4%(P<0.05). The cylinder form and rectangular form showed 41.2 and 31.6% respectively. And then the growth of the spat of arkshell was observed for 163 days by rearing in a sort of preventive net, the first group was in a blackout curtain with average shell length of $13.9{\pm}3.1$ mm, the next group was in a balsam pear net with $12.9{\pm}3.0$ mm, in a polyethylene net with $11.8{\pm}3.1$ mm and the control with $12.6{\pm}3.3$ mm which was not installed by preventive net of spat loss. The survival rate was 91.5% in a blackout curtain, 90.1% in a polyethylene net, 88.5% in a balsam pear net and 61.5% in a controlled group. It is seen that the highest growth and survival rate were observed in a fish pot form and cylinder form. These results were a little bit difference from those of the spat of arkshell cultured in the form of different preventive nets. There was no significant difference in survival rate in relation to the sorts of preventive net against carrying-away, but there was a difference in survival rate by more than 30% as against the non-installed controlled group. We expect that survival rate would be highly improved in intermediate culture carried out with fish pot form and cylinder form of protective net and preventive net of spat loss.