1,722,282 research outputs found
Blank design and strain prediction of automobile stamping parts by an inverse finite element approach
No full textA new finite element approach is introduced for direct prediction of blank shapes and strain distributions from desired final shapes in sheet metal forming. The approach deals with the geometric compatibility of finite elements, plastic deformation theory, minimization of plastic work with constraints, and a proper initial guess. The algorithm developed is applied to automobile stamping parts such as an oil pan and a front fender in order to confirm its versatility of application by demonstrating the reasonable numerical results in stamping processes. Rapid calculation with this algorithm enables easy determination of various process variables for design of sheet metal forming process
Three dimensional multi-step inverse analysis for the optimum blank design in sheet metal forming processes
No full textAn inverse finite element approach is employed for more capability to design the optimum blank shape from the desired final shape. Since one-step analysis is not accurate enough to calculate the initial blank shape for complicated parts, multi-step analysis is introduced to obtain more accurate blank shapes and strain distribution. Multi-step analysis deals with the sliding surface for intermediate shapes and the coordinate transformation for appropriate Newton-Raphson iterations. The present algorithm has been applied to square cup drawing and oil-pan drawing. The numerical results confirm the validity and versatility of the algorithm with the initial blank shapes calculated and comparison to experimental results. (C) 1998 Elsevier Science S.A. All rights reserved
Subspace-based online calibration algorithm for an asynchronous CDMA-based antenna array
No full textResidual stress effect on self-annealing of electroplated copper
No full textThe remarkable feature of electroplated film was grain growth at room temperature and this phenomenon was named 'self-annealing'. The driving force of self-annealing was expected as highly increased defect and surface energy, but the exact mechanism was unknown. In this work, residual stress effect on self-annealing was investigated. During self-annealing, increased temperature accelerated grain growth, and it is concluded that self-annealing is caused by Cu grain boundary diffusion. From the stress measurement by X-ray difractometer (XRD), it was the shown that the average stress release was 500 MPa during self-annealing. The average strain energy is lower than the grain boundary energy, but locally high stress originated from trapped poly ethylene glycol (PEG) whose molecular size is large at the grain boundary, can accelerate grain boundary diffusion of Cu. Therefore, stress is major,driving force of self-annealing, and it plays a role in decomposing PEG molecules and providing sufficient driving force for grain boundary diffusion to Cu atoms near PEG.This work was supported by grant No. 1999-2-301-008-2 from the Basic Research Program of the Korea Science & Engineering Foundation
Aluminum-seeded growth of microcrystalline Si thin film onto SnO2 substrate
No full textTo improve the crystallinity of thin boron-doped microcrystalline Si (p-mu c-Si:H) films at an initial growth stage, we tried an Al-seeding method, which is to deposit an ultrathin (similar to 50 Angstrom) Al layer onto a transparent conducting oxide before preparing the p-mu c-Si:H film by using a mercury-sensitized photochemical vapor deposition method. It was found that the Al layer serves as seeds to facilitate the p-mu c-Si:H with high crystallinity at an initial growth stage and the Al seeds stimulate the nucleation of Si crystallites. It was also found that the absorption loss in the ultrathin (similar to 50 A) Al-seed layer is negligible in the visible wavelength region due to its natural oxidation. When used in superstrate-type p-i-n amorphous silicon solar cells, even the Al-seeded p-mu c-Si:H film having a several hundred angstrom thickness acts as an excellent p layer compared to the conventional p-mu c-Si:H. (C) 2000 American Institute of Physics. [S0003- 6951(00)03239-3]
Effect of operating variables on the flux and selectivity in sweep gas membrane distillation for dilute aqueous isopropanol
No full textSweep gas membrane distillation was examined as a possible technique for isopropanol (IPA)-water separation using PTFE hollow fiber membrane module. The composition and flux of the permeate were monitored when feed concentration, operating temperature and flow late were varied. The upper feed concentration tested was 10 wt.% IPA. Within the feed temperature range of about 20-50 degreesC, IPA selectivity of 10-25 was achieved. Since the concentration near the surface on the membrane increased by the selective adsorption of IPA on the hydrophobic membrane, the selectivity increases. The permeate flux and IPA selectivity increase as feed temperature increase. The flux and selectivity increase at higher how rates is mainly due to the reduced effects of concentration and temperature polarization. The effect of salt addition to the feed mixture was also examined. (C) 2001 Elsevier Science B.V. All rights reserved.This work was supported by Grant No. 971-4401-049-2 from the Basic Research program of the KOSEF and also partially supported by the Brain Korea 21 Project
Geometric attack resistant watermarking in wavelet transform domain
No full textIn this paper, we propose an autocorrelation function (ACF) based watermarking scheme in the discrete wavelet transform (DWT) domain. Conventional ACF-based watermarking embeds a watermark in the spatial domain due to its detection mechanism. We show that the autocorrelation (AC) peaks, which play an important role in estimating the applied geometric attacks in ACF-based watermarking, can also be extracted by embedding the watermark in the DWT domain. In the proposed scheme, a periodic watermark is embedded in the DWT domain by considering the AC peak strength and noise visibility. The proposed scheme also deals efficiently with the image shift problem in the detection process by using the undecimated DWT. Experimental results show that the proposed scheme yields stronger AC peaks than the spatial domain scheme does and, as a result, shows improved robustness against combined geometric-removal attacks. (C) 2005 Optical Society of America
Spin-up of a double-diffusive fluid in a cylinder
No full textA numerical study is made of the linearized spin-up process of a double-diffusive fluid in a vertically mounted cylindrical vessel of aspect ratio 0(1). Both the temperature and concentration conditions render gravitationally stable contributions to the overall density profile. Numerical solutions are acquired to the time-dependent axisymmetric Navier-Stokes equations, using the standard Boussinesq fluid approximations. The major nondimensional parameters are identified. Results are compiled for small Ekman number, the Prandtl number similar to 0(1), and broad ranges of the stratification number St, buoyancy ratio R-p, and Lewis number Le, are dealt with. The evolution of the azimuthal velocities is described, and the attendant meridional flows are depicted. The global spin-up process is retarded for a double-diffusive fluid, and this trend is more pronounced as R-p increases. The spatial nonuniformity of the rate of spin-up is enhanced as St and R-p increase. The effects of double-diffusion on the fields of perturbation density, temperature, and concentration are plotted. The impact of Le on spin-up is illustrated, and the plots of the perturbation physical variables of interest are presented. (C) 1997 by Elsevier Science Inc
Improved autocorrelation function based watermarking with side information
No full textWe propose an improved autocorrelation function (ACF)based image watermarking that is robust to combined geometric and removal attacks. ACF-based watermarking is thought of as one of the most effective watermarking schemes that resist geometric attacks. In this watermarking scheme, the autocorrelation peaks of the watermark play an important role for geometric attack estimation. The peaks, however, are vulnerable to attacks. The proposed scheme enhances the performance of ACF-based watermarking by improving the strength of the peaks. The information of an original image is used at the embedding time, so that the detector can extract strong autocorrelation peaks. Experimental results show that the proposed scheme yields better robustness than conventional ACF based watermarking against combined geometric-removal attacks. 2005 SPIE and IS&T
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