• Structural Engineering and Mechanics
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• v.74 no.4
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• pp.547-557
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• 2020

In this paper, an automatic adaptive mesh refinement procedure is presented for two-dimensional problems on the basis of a new probabilistic error estimator. First-order perturbation theory is employed to determine the lower and upper bounds of the structural displacements and stresses considering uncertainties in geometric sizes, material properties and loading conditions. A new probabilistic error estimator is proposed to reduce the mesh dependency of the responses dispersion. The suggested error estimator neglects the refinement at the critical points with stress concentration. Therefore, the proposed strategy is combined with the classic adaptive mesh refinement to achieve an optimal mesh refined properly in regions with either high gradients or high dispersion of the responses. Several numerical examples are illustrated to demonstrate the efficiency, accuracy and robustness of the proposed computational algorithm and the results are compared with the classic adaptive mesh refinement strategy described in the literature.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.127-136
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• 2008

For mobile wireless systems with full frequency reuse, co-channel interference near the cell coverage boundaries has a significant impact on the signal reception performance. This paper addresses an approach to efficiently mitigate the effect of downlink co-channel interference when multi-antenna terminals are used in cellular environments, by proposing a signal detection strategy combined with a system-level coordination for dynamic frequency reuse. We demonstrate the utilization of multi-antennas to perform spatial demultiplexing of both the desired signal and interfering signals from adjacent cells results in significant improvement of spectral efficiency compared to the maximal ratio combining (MRC) performance, especially when an appropriate frequency reuse based on the traffic loading condition is coordinated among cells. Both analytic expressions for the capacity and experimental results using the adaptive modulation and coding (AMC) are used to confirm the performance gain. The robustness of the proposed scheme against varying operational conditions such as the channel estimation error and shadowing effects are also verified by simulation results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1802-1812
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• 2001

The theoretical method is developed to investigate the effects of ring stiffeners on free vibration characteristics and transient response for the ring stiffened composite cylindrical shells subjected to the impulse pressure Loading. In the theoretical procedure, the Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The concentric or eccentric ring stiffeners are laminated with composite and have the uniform rectangular cross section. The modal analysis technique is used to develop the analytical solutions of the transient problem. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The results are verified by comparison with FEM results.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.1
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• pp.32-37
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• 2002

The use of hexagonal ceramic inserts for copper extrusion dies offers significant technical and economic advantages over other forms of manufacture. In this paper the data on the loading of the tools is determined from a commercial FEM package as the contact stress distribution on the die-workpiece interface and as temperature distributions in the die. This data can be processed as load input data for a finite element die-stress analysis. Process simulation and stress analysis are thus combined during the design and a data exchange program has been developed that enables optimal design of the dies taking into account the elastic deflections generated in shrink fitting the die inserts and that caused by the stresses generated in the process. The stress analysis of the dies is used to determine the stress conditions on the ceramic insert by considering contact and interference effects under both mechanical and thermal loads.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.72-77
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• 2001

The use of hexagonal ceramic inserts for copper extrusion dies offers significant technical and economic advantages over other forms of manufacture. In this paper the data on the loading of the tools is determined from a commercial FEM package as the contact stress distribution on the die-workpiece interface and as temperature distributions in the die. This data can be processed as load input data for a finite element die-stress analysis. Process simulation and stress analysis are thus combined during the design, and a data exchange program has been developed that enables optimal design of the dies taking into account the elastic deflections generated in shrink fitting the die inserts and that caused by the stresses generated in the process. The stress analysis of the dies is used to determine the stress conditions on the ceramic insert by considering contact and interference effects under both mechanical and thermal loads.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.230-239
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• 2004

A compact model approach of a network of spring elements for elastic loading is presented for the thermal deformation analysis of BGA package assembly. High-sensitivity moire interferometry is applied to evaluate and calibrated the model quantitatively. Two ball grid array (BGA) package assemblies are employed for moire experiments. For a package assembly with a small global bending, the spring model can predict the boundary conditions of the critical solder ball excellently well. For a package assembly with a large global bending, however, the relative displacements determined by spring model agree well with that by experiment after accounting for the rigid-body rotation. The shear strain results of the FEM with the input from the calibrated compact spring model agree reasonably well with the experimental data. The results imply that the combined approach of the compact spring model and the local FE analysis is an effective way to predict strains and stresses and to determine solder damage of the critical solder ball.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.883-888
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• 2001

The theoretical method is developed to investigate the effects of ring stiffeners on free vibration characteristics and transient response for the ring stiffened composite cylindrical shells subjected to the impulse pressure loading. In the theoretical procedure, the Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The concentric or eccentric ring stiffeners are laminated with composite and have the uniform rectangular cross section. The modal analysis technique is used to develop the analytical solutions of the transient problem. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The theoretical results are verified by comparison with FEM results.

• Journal of Korean Society on Water Environment
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• v.30 no.5
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• pp.517-523
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• 2014

In order to remove both nitrate and sulfate present in the concentrate of RO(reverse osmosis) process, a combined bio-regeneration and ion-exchange(IX) system was studied. For this purpose, both denitrifying bacteria(DNB) and sulfate reducing bacteria(SRB) were simultaneously cultivated in a bio-reactor under anaerobic conditions. When the IX column containing a nitrate-selective A520E resin was fully exhausted by nitrate and sulfate, the IX column was bio-regenerated by pumping the supernatant of the bio-reactor, which contains MLSS concentration of $125{\pm}25mg/L$, at the flowrate of 360 BV/hr. Even though the nitrate-selective A520E resin was used, the breakthrough curves of ionic species showed that sulfate was exhausted earlier than nitrate. The reason for this result is due to the fact that the concentration of sulfate in RO concentrate was 36 to 48 times higher than nitrate. The bio-reactor was successfully operated at a volumetric loading rate of 0.6 g $COD/l{\cdot}d$, nitrate-N loading rate of 0.13 g $NO_3{^-}-N/l{\cdot}d$, and sulfate loading rate of 0.08 g $SO_4{^{2-}}/l{\cdot}d$. The removal rate of SCOD, nitrate-N, sulfate was 90, 100, and 85%, respectively. When the virgin resin was fully exhausted and consecutively bio-regenerated for 2 days, 81% of nitrate and 93% of sulfate were reduced. When the virgin resin was repeatedly used up to 4 cycles of service and bio-regeneration, the ion-exchange capacity of bio-regenerated resin decreased to 95, 91, 88, and 81% of virgin resin.

• International Journal of Automotive Technology
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• v.4 no.1
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• pp.31-40
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• 2003

W-beam guardrail system has been the most popular roadside safety device around the world. Through large plastic deformation and corresponding energy dissipation, a W-beam guardrail system contains and re-directs out-of-control vehicles so as to reduce the impact damage on the vehicle occupants and the vehicles themselves. In this paper, our recent experiments on 1 : 3.75 downscaled W-beam and the beam-post system are reported. The static and impact test results on the load characteristics, the global response and the local cross-sectional distortion are reveled. The effects of three different end-boundary conditions for the beam-only testing are examined. It is found that the load characteristics are much dependent on the combined contribution of the local cross-sectional distortion and the end-supporting conditions. The energy Partitioning between the beam and the supporting Posts in the beam-Post-system testing were also examined. The results showed that the energy dissipation partitioning changed with the input impact energy. Finally, a simple mass-spring model is developed to assess the dynamic response of a W-beam guardrail system in response to an impact loading. The model's prediction agrees well with the experimental results.

• Steel and Composite Structures
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• v.10 no.1
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• pp.23-43
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• 2010

In this paper, a nonlinear model is developed using the component method in order to represent the response of steel connections under various loading conditions and temperature variations. The model is capable of depicting the behaviour of a number of typical connection types including endplate forms (extended and flush) and angle configurations (double web, top and seat, and combined top-seat-web) in both steel and composite framed structures. The implementation is undertaken within the finite element program ADAPTIC, which accounts for material and geometric nonlinearities. Verification of the proposed connection model is carried out by comparing analytical simulations with available results of isolated joint tests for the ambient case, and isolated joint as well as sub-frame tests for elevated temperature conditions. The findings illustrate the reliability and efficiency of the proposed model in capturing the stiffness and strength properties of connections, hence highlighting the adequacy of the component approach in simulating the overall joint behaviour at elevated temperature.