• Journal of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.29-40
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• 1993

The fundamental characteristics of nonlinear free-surface waves generated by a shallowly submerged 3-dimensional hydrofoil are investigated. The fluid is assumed inviscid, incompressible and its motion irrotational. The surface tension on the free-surface is neglected. The hydrofoil is represented by a horseshoe vortex system whose shape is assumed fixed. Also the strengths of vortices are assumed given. The exact problem for the wave potential due to the horseshoe vortex system is formulated by the variational principle based on the classical Hamilton's principle. The localized finite element method is used in the numerical computations. In order to increase the numerical efficiency, an intermediate nonlinear-to-linear transition buffer subdomain for a smooth matching is introduced between the fully nonlinear computation subdomain and the truncated linear infinite subdomain. Also used is the modal analysis to reduce the computation tome drastically. The effect of inflow velocity, submergence depth of the hydrofoil and the shape of circulation distribution on the wave profiles are thoroughly examined. Especially it was possible to investigate the nonlinear influence of the free vortex on the free vortex. The nonlinear free-surface effect on the induced forces on the hydrofoil is also investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.1-13
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• 1982

Transition process of plastic region. displacements, stresses and strains ahead the flaw tips were analysed by the finite element method on the steel plate with the circular hole and the one with the elliptical hole under completely alternating load (repetition of tensile loading, unloading and compressive loading). As the results, the followings were obtained. Transition process of elastic failure (yielding) region was estimated. From this the tendency was confirmed that the fracture would be initiated from ahead the flaw tip, and propagated along the $45^{\circ}$ direction. The fundamental data available in estimating the stress intensity factor that was considered as the core in analysing the fracture mechanism of steel plates were obtained. It was indicated that when unloading after tension the effect of compressive loading, and even the compressive reyield, was occured ahead the flaw tip. Similarly it was indicated that when unloading after compression the effect of tensile loading, and even the tensile reyield, was occured ahead the flaw tip. It was considered that these phenomena were occured because the unloading effect was constrained by the residual strains when unloading. It was considered that the fatigue phenomenon was occured ahead, the flaw tip by repetition of tensile yield, the above compressive reyield, compressive yeild and the above tensile reyield. In addition, the tendency was confirmed that the fracture ahead the flaw tip was occured as the flaw was changed from the circular hole to the elliptical hole and became to be the crack lastly.

• Composites Research
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• v.18 no.2
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• pp.20-29
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• 2005

To evaluate the flexural deformation and strength of composite motor case above the glass transition temperature$(T_g),\;170^{\circ}C$, of resin material, a finite element analysis(FEA) model in which material non-linearity and progressive failure mode were considered was proposed. The laminated flexural specimens which have the same lay-up and thickness as the composite motor case were tested by 4-point bending test to verify the validity of FEA model. Also. mechanical properties in high temperature were evaluated to obtain the input values for FEA. Because the material properties related to resin material were highly deteriorated in the temperature range beyond $T_g$, the flexural stiffness and strength of laminated flexural specimen in $200^{\circ}C$ were degraded by also $70\%\;and\;80\%$ in comparison with normal temperature results. Above $T_g$, the failure mode was changed from progressive failure mode initiated by matrix cracking at $90^{\circ}$ ply in bottom side and terminated by delamination at the center line of specimen to fiber compressive breakage mode at top side. From stress analysis, the progressive failure mechanism was well verified and the predicted bending stiffness and strength showed a good agreement with the test results.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.1
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• pp.31-39
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• 2014

For mobile application, semiconductor packages are increasingly moving toward high density, miniaturization, lighter and multi-functions. Typical wafer level packages (WLP) is fan-in design, it can not meet high I/O requirement. The fan-out wafer level packages (FOWLPs) with reconfiguration technology have recently emerged as a new WLP technology. In FOWLP, warpage is one of the most critical issues since the thickness of FOWLP is thinner than traditional IC package and warpage of WLP is much larger than the die level package. Warpage affects the throughput and yield of the next manufacturing process as well as wafer handling and fabrication processability. In this study, we investigated the characteristics of warpage and main parameters which affect the warpage deformation of FOWLP using the finite element numerical simulation. In order to minimize the warpage, the characteristics of warpage for various epoxy mold compounds (EMCs) and carrier materials are investigated, and DOE optimization is also performed. In particular, warpage after EMC molding and after carrier detachment process were analyzed respectively. The simulation results indicate that the most influential factor on warpage is CTE of EMC after molding process. EMC material of low CTE and high Tg (glass transition temperature) will reduce the warpage. For carrier material, Alloy42 shows the lowest warpage. Therefore, considering the cost, oxidation and thermal conductivity, Alloy42 or SUS304 is recommend for a carrier material.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.65-72
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• 1993

A numerical method for nonlinear free-surface-wave problem is developed in this paper. The final goal of this study is to simulate the towing tank experiment of a ship model and to partially replace the experiment by the numerical model. The exact problem in the scope of potential flow theory is formulated by a variational principle based on the classical Hamilton's principle. A localized finite element method is used in the present numerical computations which made use of the following two notable steps. The first step is an efficient treatment of the numerical radiation condition by using the intermediate nonlinear-to-linear transition buffer subdomain between the fully nonlinear and linear subdomains. The second is the use of a modal analysis in the final stage of the solution procedures, which enables us to reduce the computation time drastically. With these improvements the present method can treat a much larger computational domain than that was possible previously. A pressure patch on the free surface was chosen as an example. From the present computed results we could investigate the effect of nonlinearity on the down-stream wave pattern more clearly than others, because much larger computational domain was treated. We found, specifically, the widening of the Kelvin angle and the increase of the wave numbers and the magnitude of wave profiles.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.2
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• pp.17-28
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• 2012

It is known that thermo-mechanical properties of solder material and molding compound in WB-PBGA packages are considerably affected by not only temperature but elapsed time. In this paper, finite element analysis (FEA) taking material nonlinearity into account was performed for more reliable prediction on deformation behavior of a lead-free WB-PBGA package, and the results were compared with experimental results from moire interferometry. Prior to FEA on the WB-PBGA package, it was carried out for two material layers consisting of molding compound and substrate in terms of temperature and time-dependent viscoelastic effects of molding compound. Reliable deformation analysis for temperature change was then accomplished using viscoplastic properties for solder ball and viscoelastic properties for molding compound, and the analysis was also verified with experimental results. The result showed that the deformation of WB-PBGA packages was strongly dependent on material model of molding compound; thus, temperature and time-dependent viscoelastic behavior must be considered for the molding compound analysis. In addition, viscoelastic properties of B-type molding compound having comparatively high glass transition temperature of $135^{\circ}C$ could be recommended for reliable prediction on deformation of SAC lead-free WB-PBGA packages.