• Transactions of Materials Processing
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• v.11 no.6
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• pp.487-494
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• 2002

A new method of optimal blank shape design using the initial nodal velocity (INOV) has been proposed for the drawings of arbitrary shaped cups. With the given information of tool shape and the final product shape, corresponding initial blank shape has been found from the motion of boundary nodes. Although the sensitivity method, the past work of the present authors, has been proved to be excellent method to find optimal blank shapes, the method has a problem that a couple of deformation analysis is required at each design step and it also exhibits an abnormal behaviors in the rigid body rotation prevailing region. In the present method INOV, only a single deformation analysis per each design stage is required. Drawings of practical products as well as oil-pan, have been chosen as the examples. At every case the optimal blank shapes have been obtained only after a few times of modification without predetermined deformation path. The deformed shape with predicted optimal blank almost coincides with the target shape at every case. Through the investigation the INOV is found to be very effective in the arbitrary shaped drawing process design.

• Geomechanics and Engineering
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• v.11 no.6
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• pp.739-756
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• 2016

The shear strength reduction finite element method (SSRFEM) is a powerful tool for slope stability analysis. The factor of safety (FOS) of the slope can be easily calculated only through reducing effective cohesion (c′) and tangent of effective friction angle ($tan{\varphi}^{\prime}$) in equal proportion. However, this method may not be applicable to soil slope under wetting-drying cycles (WDCs), because the influence of WDCs on c′ and $tan{\varphi}^{\prime}$ may be different. To research the method of estimating FOS of soil slopes under WDCs, this paper presents an experimental study firstly to investigate the effects of WDCs on the parameters of shear strength and stiffness. Twelve silty clay samples were subjected to different number of WDCs and then tested with triaxial test equipment. The test results show that WDCs have a degradation effect on shear strength (${\sigma}_1-{\sigma}_3)_f$, secant modulus of elasticity ($E_s$) and c′ while little influence on ${\varphi}^{\prime}$. Hence, conventional SSRFEM which reduces c′ and $tan{\varphi}^{\prime}$ in equal proportion cannot be adopted to compute the FOS of slope under conditions of WDCs. The SSRFEM should be modified. In detail, c′ is merely reduced among shear strength parameters, and elasticity modulus is reduced correspondingly. Besides, a new approach based on sudden substantial changes in the displacement of marked nodes is proposed to identify the slope failure in SSRFEM. Finally, the modified SSRFEM is applied to compute the FOS of a slope example.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.124-127
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• 2005

As computer capability and test skill become more and more advanced, finite element method and modal test are being widely applied in engineering design. In order to correlate and reconcile the inevitable discrepancies between the analytical and experimental models, many techniques have been developed. Among these methods, multiple-system methods are known as the effective tools in that they can supply the rich modal data available which are experimentally obtained. These abundant modal data can help structural system parameters estimated well. Multiple-system methods can be classified into the structural modification methods and feedback controller methods. The structural modification methods need the physical attachment of structures and their concept may limit the application of them. To overcome this drawback, the feedback controller methods are addressed which enable us to get more modal data without the structural change. Mode decoupling controller(MDC), one of them, is to use acceleration out)ut feedback to perturb an open-loop system. The output feedback controller generally cannot guarantee the stability of a closed-loop system. However, MDC can solve this problem under the certain constraints. So far, MDC utilizes accelerations as the sensor signals. In this research, strain sensors are going to be picked up to apply to the MDC. Strain output is recently used for structural system identification due to the drastically improved and miniaturized strain sensor. In this paper, we show that the MDC using strain output has differences compared with acceleration output in estimating the structural system parameters. The associated simulation is performed to demonstrate the above mentioned characteristics.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.115-123
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• 1989

A computer program evaluating the pile downdrag is developed using the conventional elastic solid method. Modification of the conventional method has been performed by introducing the concept of critical relative displacement. A simple transfer function method which employes the critical relative displacement as a pile-soil slip criterion and calculates downdrag by Mohr-Coulomb equation, has also been developed. The results of three methods are all found to be in good agreement with field observations. When they are applied to a centrifuge modeling problem of pile downdrag to predict its result, however, diverse answers are obtained. Overall, the simple transfer function method developed in this study seems to be the most effective in the evaluation of pile downdrag, considering the quality of its result and its efficiency in computation.

• Journal of Surface Science and Engineering
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• v.35 no.5
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• pp.319-324
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• 2002

It is known that ion-assisted reaction method is effective for the surface modification of polymers. The surface treatment of Spectra fibers using the ion-assisted reaction method was investigated in the present study The Spectra fibers were treated by $Ar^{+}$ / ion irradiation under oxygen environment. The treatment was carried out at different $Ar^{+}$ ion doses. The$ Ar^{+ }$ /ion doses used were $6$\times$10^{15}$ , $1$\times$10^{16}$ , $5$\times$10^{16}$ , $1$\times$10^{17}$ / ions/$\m^2$. Optimal $Ar^{+}$ ion dose in the treatment of Spectra fibers was determined by measuring the tensile strength and modulus of Spectra/vinylester composites as a function of ion dose. It was found that the optimal ion dose was $1$\times$10^{16}$ions/$\m^2$. It was also found from the scanning electron microscope examination that the surface-treatment improved adhesion between fibers and vinylester resin.

• Tribology and Lubricants
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• v.24 no.3
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• pp.122-128
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• 2008

To reduce the friction losses and the wear amounts in the piston assembly two methods were proposed. One is the modification of surface profile of the skirt part. The surface coating is another method to protect the sliding surfaces. To modify the profile of the skirt surfaces the surfaces were ground to have three different shapes of profiles. Also, several coatings, such as graphite, TiN, and $MoS_2$, and DLC, were used to protect the surfaces of the piston skirts. The specimens of the skirt and the cylinder bores were tested with the reciprocating wear tester. SAE 5W40 engine oil was used in boundary lubrication regime. Among several coatings the graphite and DLC coatings were very effective to reduce the friction forces. Especially, DLC film represented much better tribological performances than the others. The friction coefficient of the graphite coating was the lowest, but the graphite coating was not effective to protect the surfaces.

• Korean Journal of Materials Research
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• v.19 no.3
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• pp.156-162
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• 2009

Lubricant-based nanofluids were prepared by dispersing carbon nanoparticles in gear oil. In this study, the effects of the particle size, shape and dispersity of the particles on the tribological properties of nanofluids were investigated. Dispersion experiments were conducted with a high-speed bead mill and an ultrasonic homogenizer, and the surfaces of the nanoparticles were simultaneously modified with several dispersants. The effective thermal conductivity of the nanofluids was measured by the transient hot-wire method, and the tribological behaviors of the nanofluids were also investigated with a disk-on-disk tribo-tester. The results of this study clearly showed that the combination of the nanoparticles, the deagglomeration process, the dispersant and the dispersion solvent is very important for the dispersity and tribological properties of nanofluids. Lubricant-based nanofluids showed relatively low thermal conductivity enhancement, but they were highly effective in decreasing the frictional heat that was generated. For nanofluids containing 0.1vol.% graphite particles in an oil lubricant, The friction coefficient in the boundary and fluid lubrication range was reduced to approximately 70% of the original value of pure lubricant.

• Journal of Agricultural Extension & Community Development
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• v.5 no.1
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• pp.11-30
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• 1998

The lack of close working relationship between agricultural research, extension organizations and farmers, is one of the most difficult problems confronting agricultural technology system. Systems approach is an effective method to use in indentifying lingkage problems in agricultural technology system, and it is a problem-solving methodology. There are two basic types of linkage mechanisms; organizational and managerial. Organizational mechanisms involve the structural modification of the research and extension organizations involved in an agricultural technology system. The other major type of lingkage mechanisms involves a range of managerial interventions such as joint planning and review activities, collaborative program activities, and resource allocation procedures, etc.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.191.2-191.2
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• 2010

The conventional method to assess turbine performance is its model testing which becomes costly and time consuming for several design alternatives in design optimization. Computational fluid dynamics (CFD) has become a cost effective tool for predicting detailed flow information in turbine space to enable the selection of best design. In the present paper, Francis turbine of commercial small hydropower plants which is under 70kw is investigated. Solutions are investigated with respect to the hydraulic characteristics against an outward angle of guide vane, the number of guide vane and head (inlet velocity). By suitable modification of the runner shape, low pressure zone on the leading edge can be reduced. If the entire runner is to be optimized in this manner, flow simulation tests have to be carried out on a series of different geometrical shape.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.3
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• pp.90-96
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• 1995

In general, natural gas engine converted from gasoline engine has disadvantage of power decrease. In order to increase power output in natural gas engine, the improvement of in-cylinder flow motion has been believed as the most effective method. In this study, the geometry of combustion chamber in 4 valve DOHC natural gas engine is modified, and in-cylinder flow patterns is analyized. Also engine performance is evaluated according to the modification of in-cylinder flow motion.