• Transactions of Materials Processing
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• v.21 no.8
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• pp.479-484
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• 2012

The objective of this study is to compensate the elastic recovery in the flexible forming process using the predictive models. The target shape was limited to two-dimensional shape having only one curvature radius in the longitudinal-direction. In order to predict the shape error the regression and neural network models were established based on the finite element (FE) simulations. A series of simulations were conducted considering input variables such as the elastic pad thickness, the thickness of plate, and the objective curvature radius. Then, at sampling points in the longitudinal-direction, the shape errors between formed and objective shapes could be calculated from the FE simulations as an output variable. These shape errors were expressed to a representative error value by the root mean square error (RMSE). To obtain the correct objective shape the die shape was adjusted by the closed-loop using the neural network model since the neural network model shows a higher capability of estimating the shape error than the regression model. Finally the experimental result shows that the formed shape almost agreed with the objective shape.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.493-494
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• 2010

• Transactions of Materials Processing
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• v.22 no.4
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• pp.196-203
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• 2013

Flexible stretch forming is an appropriate process for manufacturing of components for aerospace, shipbuilding and architecture structures. Flexible stretch forming has several advantages including that it could be applied to form various shapes such as ones with double curved surfaces. In this study, a systematic numerical simulation was conducted for forming double curved surfaces using flexible stretch forming. The desired surface had a saddle type configuration. It had two radii one of 2500mm and the other of 2000mm along its length and width. In the simulation, the decrease of elastic recovery due to the stretching was confirmed. Experiments were also conducted to confirm the viability of the process. By comparing the simulation to the experiment results, the suitability of flexible stretch forming for double curved surfaces was verified. From the results, the maximum error from desired surface was confirmed at about 1.3mm at the edge of the surface. Hence, it is confirmed that flexible stretch forming has the capability and feasibility to manufacture curved surfaces for architectural skin-structures of buildings.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.15-21
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• 2001

An accumulator in hydraulic systems stores kinetic energy during braking action, and then that controls hasty surge pressure. An energy recovery system using accumulator seems to be advantageous for ERBS due to its high energy density. This study suggests a method to decide suitable accumulator volume for ERBS. The method is based upon energy conservation between kinetic energy of moving inertia and elastic energy of accumulator. The energy conversion was analyzed and a simple formula was derived. A series of computer simulation was done to verify effectiveness of the formula. The results of the simulation work were compared with those of experiments and these results show that the proposed design is effective for decision accumulator volume in ERBS.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.1
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• pp.104-113
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• 2002

An accumulator in hydraulic systems stores kinetic energy during braking action and then that controls hasty surge pressure. An energy recovery system using accumulator seems to be advantageous far ERBS due to its high energy density. This study suggests a method to decide suitable accumulator volume far ERBS. The method is based upon energy conservation between kinetic energy of moving inertia and elastic energy of accumulator. The energy conversion was analyzed and a simple formula was derived. A series of computer simulation was done to verify effectiveness of the formu1a. The results of the simulation work were compared with those of experiments and these results show that the proposed design is effective far decision of accumulator volume in ERBS.

• Ocean Systems Engineering
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• v.4 no.3
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• pp.215-241
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• 2014

Steel catenary riser (SCR) is a popular/economical solution for the oil/gas production in deep and ultra-deep water. The behavioral characteristics of SCR have a high correlation with the motion of floating production facility at its survival and operational environments. When large motions of surface floaters occur, such as FPSO in 100-yr storm case, they can cause unacceptable negative tension on SCR near TDZ (touch down zone) and the corresponding elastic deflection can be large due to local dynamic buckling. The generation, propagation, and decay of the elastic wave are also affected by SCR and seabed soil interaction effects. The temporary local dynamic buckling vanishes with the recovery of tension on SCR with the upheaval motion of surface floater. Unlike larger-scale, an-order-of-magnitude longer period global buckling driven by heat and pressure variations in subsea pipelines, the sub-critical local dynamic buckling of SCR is motion-driven and short cycled, which, however, can lead to permanent structural damage when the resulting stress is greatly amplified beyond the elastic limit. The phenomenon is extensively investigated in this paper by using the vessel-mooring-riser coupled dynamic analysis program. It is found that the moment of large downward heave motion at the farthest-horizontal-offset position is the most dangerous for the local dynamic buckling.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.300-301
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• 2007

In this study, it is investigated that sheet characteristics of high strength steel sheets and effect of springback. High strength steel sheets has got attention in automobile industry of high strength and high formability. Springback is a common phenomenon in sheet metal forming, caused by the elastic recovery of the internal stresses after removal of the tooling. However, the information in deformation behavior of high strength steel sheets, including bending and sheet characteristics and springback, is not enough until now. In this research, the V-bending experiment and analysis have been done to obtain the information of springback of high strength steel sheets. Tensile test for high strength steel sheets was done to got tensile properties of elastic modulus and flow stress of the material. It analyzed springback according to the sheet characteristics with using roll-forming model. FE-Simulation used DEFORM-$3D^{TM}$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.245-248
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• 2008

This paper deals with the parameter study of roller leveling process of steel cord using finite element analysis. A simplified model of roller leveling process is constructed for the efficient numerical simulation considering the computing time. Using the constructed simulation scheme, the parameter study of main process parameters, such as back-tension and intermesh, is carried out in order to evaluate elastic recovery angle and roller force quantitatively. The effect of the initial shape of steel cord is also evaluated during the parameter study. And the mechanism of roller leveling process is verified by investigating the residual stress distribution.

• Tribology and Lubricants
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• v.22 no.5
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• pp.243-251
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• 2006

Molecular dynamics simulations of nanoimprint lithography NIL) are performed in order to investigate effects of process parameters, such as stamp shape, imprinting temperature and adhesive energy, on nanoimprint lithography process and pattern transfer. The simulation model consists of an amorphous $SiO_{2}$ stamp with line pattern, an amorphous poly-(methylmethacrylate) (PMMA) film and an Si substrate under periodic boundary condition in horizontal direction to represent a real NIL process imprinting long line patterns. The pattern transfer behavior and its related phenomena are investigated by analyzing polymer deformation characteristics, stress distribution and imprinting force. In addition, their dependency on the process parameters are also discussed by varying stamp pattern shapes, adhesive energy between stamp and polymer film, and imprinting temperature. Simulation results indicate that triangular pattern has advantages of low imprinting force, small elastic recovery after separation, and low pattern failure. Adhesive energy between surface is found to be critical to successful pattern transfer without pattern failure. Finally, high imprinting temperature above glass transition temperature reduces the imprinting force.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1511-1516
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• 2007

Because Seaming process of MPJ (Mechanical Press Joining) has various design factors such as thickness, bending radius, seaming width, caulking press width and the dynamic factor such as multistage plastic working, elastic recovery, residual stress, the optimum conditions can't be easily determined. Using a design of experiment based on the FEM, which has several advantages such as less computing, high accuracy performance and usefulness, this study was performed investigating the interaction effect between the various design factor as well as the main effect of the each design factor during drum MPJ and proposed optimum condition using center composition method among response surface derived from regression equation of simulation-based DOE.