• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.125.2-125.2
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• 2011

We are developing medium resolution cross-dispersed silicon grisms in the near IR region ($1.45{\sim}5.2{\mu}m$). The grisms will be installed in MIMIR, a multifunction instrument at the Lowel Observatory, USA. The two devices are designed to cover H and K band and L and M band simultaneously. Our goal is to make grism with R=3000 at 1.2 arcsec slit. The Silicon has high refractive index (n=3.4 at $1.5{\mu}m$) which enhances the resolving power by up to 5 times when compared to conventional material such as BK-7 (n=1.5 at 1.5 ${\mu}m$). The bonded grisms will be installed in a filter wheel for the uses switch from spectroscopic mode to imaging mode easily. Our device is compact and light weighted while it provides a decent resolving power. We produce monolithic grisms using e-beam lithography at the NASA JPL and chemically etching the grooves on the silicon prisms. Moreover, the main-disperser and cross-disperser will be contacted together by direct Si-Si bonding technique and eventually turn into one piece. The bonded pair offers more stability in terms of the layout of the spectrum and removes the Fresnel loss at the intersection of two grisms. We report on the proper wafer bonding steps through this research, and inspected the bonding quality thermally, optically and mechanically.

• Elastomers and Composites
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• v.43 no.1
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• pp.25-30
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• 2008

A bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is a hollow cylinder, which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the force and moment applied to the shaft and the relative deformation and rotational angle of a bushing exhibits features of viscoelasticity. Since a moment-rotational angle relation for a bushing is important for multibody dynamics numerical simulations, the simple relation between the moment and rotational angle has been derived from experiment. It is shown that the predictions by the proposed moment-rotational angle relation are in very good agreement with the experimental results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.6
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• pp.14-20
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• 2015

A high-speed reduction transfer case is usually employed by an excavator, wheel loader, or bulldozer. When powerful torque is required in the case of climbing steep roads or towing heavy equipment, the high-speed reduction mode of the gearbox is used. Generally, a transfer case using a spur gear type with a speed reduction system has a speed reduction ratio of 1 to 1 or 2 to 1. However, the structure of a transfer case achieved at a high speed of 1 to 1 and a low speed of 4.5 or under 5.5 to 1 with the speed reduction by use of a planetary gear type with a speed reduction system was proposed in this study. By employing a planetary gear type with a speed reduction system, the compact structure of the transfer case was achieved, and the impact or the partial defect of gear teeth was eliminated.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.204-209
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• 2003

An elastomeric bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is an elastomeric hollow cylinder which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the load applied to the shaft or sleeve and the relative deformation of elastomeric bushing is nonlinear and exhibits features of viscoelasticity. A load-displacement relation for elastomeric bushing is important for dynamic numerical simulations. A boundary value problem for the bushing response leads to the load-displacement relation which requires complex calculations. Therefore, by modifying the constitutive equation fur a nonlinear viscoelastic incompressible material developed by Lianis, the data fur the elastomeric bushing material was obtained and this data was used to derive the new load-displacement relation for radial response of the bushing. After the load relaxation function for the bushing is obtained from the step displacement control test, Pipkin-Rogers model was developed, Solutions were allowed fur comparison between the results of Modified Lianis model and those of the proposed model. It is shown that the proposed Pipkin-Rogers model is in very good agreement with Modified Lianis model.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.10
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• pp.139-145
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• 1996

The machining accuracy and performance is largely influenced by the static, dynamic and thermal characteristics of spindle systems in machine tools, because the spindle system is a intermedium for cutting force from tool and machine powef from motor. Large cutting force and power are transmitted by bearing with a point or line contact. So, the spindle system is the static and dynamic weakest point in machine structure. For improvement of static stiffness of spindle system can be changed design parameters, such as diameter of spindle, stiffness of bearing and bearing span. But for dynamic stiffness, the change of the design parameters are not useful. In this paper, the combined bearing arrangement is suggested for high damping spindle system. The combined bearing arrangement is composed of tandem double back to back arrangement type ball bearins and a high damping hydrostatic bearing. The variation of static deflection and amplitude in first natural frequency is evaluated with the location of hydrostatic bearing between front and rear ball bearing. The optimized location of hydrostatic bearing for high static and dynamic stiffness is determined rapidly and exactly using the mode shape and transfer function of spindle. The calculation of damping effect on vibration by unbalance of grinding wheel and pulley in optimized spindle system is carried out to verify the validity of the combined bearing arrangement. Finally, the simulation of grinding process show that the surface roughness of workpiece with high damping spindle system is 60% better than with ball bearing spindle system.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.3
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• pp.367-373
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• 2017

In this paper, a new shift map was proposed to improve the fuel economy of a transmission mounted electric device(TMED) type dual clutch transmission(DCT) plug-in hybrid electric vehicle(PHEV) by considering transmission and motor losses. To construct the shift map, powertrain efficiencies of the engine-DCT-motor were obtained at each gear step. A shift map that provides the highest powertrain efficiency was constructed for the given wheel torque and vehicle speed. Simulation results showed that the fuel economy of the target PHEV can be improved by the new shift map compared with the existing engine optimal operating line(OOL) shift control.

• Elastomers and Composites
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• v.37 no.3
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• pp.151-158
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• 2002

An elastomeric bushing which has been considered in this research is a device used in automotive suspension systems to reduce the forte transmitted iron the wheel to the frame of the vehicle. A bushing is modeled at a hollow cylinder which is bonded to a solid metal shaft at its inner surface and a metal sleeve at its outer surface. Lianis constitutive equation for a nonlinear viscoelastic incompressible material is used to model the elastomeric material of the bushing. It is used to derive a force-displacement relation for axial response of the bushing. The displacement dependent force relaxation function for the bushing is obtained from the ramp displacement control tests with an extrapolation method. This is compared with the exact result obtained from the step displacement control test and the results are in very good agreement.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.187-193
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• 2007

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}\;-\;{\omega}$ turbulence model. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 for two-dimensional case, same aspect ratios with the W/D ratio of 2 for three-dimensional case. The Mach and Reynolds numbers are 0.53 and 1,600,000 respectively. The flow field is observed to oscillate in the "shear layer mode" with a feedback mechanism. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formula. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster.

• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1324-1331
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• 2003

A bushing is a device used in automotive suspension systems to cushion the force transmitted from the wheel to the frame of the vehicle. A bushing is essentially a hollow cylinder which is bonded to a solid metal shaft at its inner surface and a metal sleeve at its outer surface. The shaft is connected to the suspension and the sleeve is connected to the frame. The cylinder provides the cushion when it deforms due to relative motion between the shaft and sleeve. The relation between the force applied to the shaft or sleeve and its deformation is nonlinear and exhibits features of viscoelasticity. An explicit force-displacement relation has been introduced for multi-body dynamics simulations. The relation is expressed in terms of a force relaxation function and a method of determination by experiments on bushings has been developed. Solutions allow for comparison between the force-displacement behavior by experiments and that predicted by the proposed method. It is shown that the predictions by the proposed force-displacement relation are in very good agreement with the experimental results.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.415-419
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• 2003

An elastomeric bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is an elastomeric hollow cylinder which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the load applied to the shaft or sleeve and the relative deformation of elastomeric bushing is nonlinear and exhibits features of viscoelasticity. A load-displacement relation for elastomeric bushing is important for dynamic numerical simulations. A boundary value problem for the bushing response leads to the load-displacement relation which requires complex calculations. Therefore, by modifying the constitutive equation for a nonlinear viscoelastic incompressible material developed by Lianis, the data for the elastomeric bushing material was obtained and this data was used to derive the new load-displacement for radial response of the bushing. After the load relaxation function for the bushing is obtained from the step displacement control test, Pipkin-Rogers model was developed. Solutions were allowed for comparison between the results of Modified Lianis model and those of the proposed model. It is shown that the proposed Pipkin-Rogers model is in very good agreement with Modified Lianis model.