• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.154-161
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• 2004

The flat dilatometer test(DMT) is a geotechnical tool to estimate in-situ properties of various types of ground materials. The undrained shear strength is known to be the most reliable and useful parameter obtained by DMT. However, the existing relationships which were established for other local deposits depend on the regional geotechnical characteristics. In addition, the flat dilatometer test results have been interpreted using three intermediate indicesmaterial index($I_p$), horizontal stres index($K_p$), and dilatometer modulus($E_p$) and the undrained shear strength is estimated only by using the horizontal stress index($K_D$). In this paper, an artificial neural network was developed to evaluate the undrained shear strength by DMT and the ANN, based on the $p_0,\;p_1,\;p_2,\;{\sigma}'_v_0$, and porewater pressure. The ANN which adopts the back-propagation algorithm was trained based on the DMT data obtained from Korean soft clay. To investigate the feasibility of ANN model, the prediction results obtained from data which were not used to train the ANN and those obtained from existing relationships were compared.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.2
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• pp.55-61
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• 2008

This paper shows quantitative reliability evaluations of a Bluetooth module through extending previous qualitative methods limited to structure reliability tests and solder joint reliability tests for Bluetooth modules. Accelerated Life Testing (ALT) of the modules using temperature difference in temperature cycling as an accelerated stress was conducted for quantitative reliability evaluation under field environment conditions. Lifetime distribution parameters were estimated using the failure times obtained through the ALT, and then Coffin-Manson model was implemented. Results of the ALT showed that the failure mode of the modules was open and the failure mechanisms are both crack and delamination. The ALT reproduced the failure mode and mechanisms of failed Bluetooth modules collected from the field. Further, a quantitative reliability evaluation method with respect to various temperature differences in temperature cycling was proposed in this paper. $B_{10}$ lifetime of the module for the temperature difference $70^{\circ}C$ using the proposed method would be estimated as about 4 years.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.199-208
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• 1993

Using several soil parameters which are obtained from the PI-experimental formulas and the back analysis method, the elastic analysis, the elasto-plastic analysis and the elasto-viscoplastic analysis for soil deformation are executed. Comparing the results with those of consolidation test, the indirect estimation method for soil parameters and the suitability of constitutive models are studied. The elastic analysis using back analysis result and the elasto-plastic analysis using the perconsolidation test. The elasto-viscoplastic analysis disagrees with the results of meability coefficient obtained from back analysis are the nearest to the results of the consolidation test. It is inferred that elasto-viscoplastic model is not adequate to the soil of which plasticity index is low.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1243-1251
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• 1994

The implicit finite difference program was developed to evaluate the relationship between time and consolidation ratio within the zone of vertical drain effective radius. In the evaluation, the excess pore water pressure was considered to dissipate in two directions, namely, vertical and radial flow direction. To calculate subsoil stress increments in the soil due to multi-step embanking, the foundation soil was assumed to be an isotropic and homogeneous elastic medium and the initial excess pore water pressure was estimated by using Skempton's parameters whose condition is plane strain and elastic phase of pore pressure response within the soft ground. Regarding to the settlement estimation, immediate and primary consolidation settlements were calculated. The secondary or delayed consolidation settlement was not considered. Numerically calculated excess pore water pressure and settlements were similar to the measured data in situ. Thus, this method can be used to predict the time-consolidation ratio of each layer treated by vertical drain method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1541-1549
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• 2013

This study investigates the response of structures to tunnelling-induced ground movements in sand ground, varying tunnel excavation condition (tunnel depth and diameter), tunnel construction condition (ground loss), ground condition (loose sand and dense sand). Four-story block-bearing structures have been used because the structueres can easily be characterized of the extent of dmages with crack size and distribution. Numerical parametric studies have been used to investigae of the response of structures to varying tunnelling conditions. Numerical analysis has been conducted using Discrete Element Method (DEM) to have real cracks when the shear and tensile stress exceed the maximum shear and tensile strength. The results of structure responses from various parametric studies have been integrated to consider tunnel excavation condition, tunnel construction condition, and ground condition and provided as a relationship chart. Using the chart, the response of structures to tunnelling can easily be evaluated in practice in sand ground.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.101-111
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• 2008

Strain imaging in a medical ultrasound imaging system can differentiate the cancer or tumor in a lesion that is stiffer than the surrounding tissue. In this paper, a strain imaging technique using quasistatic compression is implemented that estimates the displacement between pre- and postcompression ultrasound echoes and obtains strain by differentiating it in the spatial direction. Displacements are computed from the phase difference of complex baseband signals obtained using their autocorrelation, and errors associated with converting the phase difference into time or distance are compensated for by taking into the center frequency variation. Also, to reduce the effect of operator's hand motion, the displacements of all scanlines are normalized with the result that satisfactory strain image quality has been obtained. These techniques have been incorporated into implementing a medical ultrasound strain imaging system that operates in real time.

• Journal of the Korean Society of Propulsion Engineers
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• v.1 no.2
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• pp.12-21
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• 1997

Nowadays, non-pollution energy sources have been strongly needed because of the exhaustion of fossil fuels and serious environmental problems. Because wind energy can be enormously obtained from natural atmosphere, this type of energy has lots of advantages in a economic and pollution point of view. This study has established the aerodynamic and structural design procedure of the rotor blade with an appropriate aerodynamic performance and structural strength for the 500㎾ medium class wind turbine system. The aerodynamic configuration of the rotor blade was determined by considering the wind condition in the typical local operation region, and based on this configuration aerodynamic performance analysis was performed. The rotor blade has the shell-spar structure based on glass/epoxy composite material and is composed of shank including metal joint parts and blade. Structural design was done by the developed design program in this study and structural analysis, for instance stress analysis, mode analysis and fatigue life estimation, was performed by the finite element method. As a result, a medium scale wind turbine rotor blade with starting characteristics of 4m/s wind speed, rated power of 500㎾ at 12m/s wind speed and over 20 years fatigue life has been designed.

• Journal of the Korean Society of Marine Environment & Safety
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• v.11 no.2 s.23
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• pp.77-82
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• 2005

Previously sailing yachts or leisure yachts were mainly made from FRP(Fiber glass reinforced plastic) in the small shipbuilding, but recently there is a trend to replace it for steel or aluminum to substitute FRP for environmental friendly materials. Although It have to need a many checked item in case of hull girder strength and transverse strength normally evaluate base on calculation of class guideline so called direct calculation method. Otherwise. this method of initial structural design considered enough for safety margin on the structure. But, case of small craft must consider for evaluating local strength through rational method. In this paper, check the bow structure members for satisfying results base on allowable stress criterion of damaged bow structure by dynamic load due to slamming and bottom impact load due to pitching motion through finite element analysis. and investigate engine bed structure considering engine weight load and transverse wave load.

• Proceedings of KOSOMES biannual meeting
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• 2004.11a
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• pp.129-135
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• 2004

Plate has cutout inner bottom and girder and floor etc in hull construction absence is used much, and this is strength in case must be situated, but establish in region that high stress interacts sometimes fatally in region that there is no big problem usually by purpose of weight reduction, a person and change of freight, piping etc. Because cutout's existence gnaws in this place, and, elastic budding strength by load rouses large effect in ultimate strength. Therefore, perforated plate elastic budding strength and ultimate strength is one of important design criteria which must examine when decide structural elements size at early structure design step if ship. Therefore, and, reasonable elastic budding strength about perforated plate need design ultimate strength. Calculated ultimate strength change several aspect ratioes and cutout's dimension, and thickness in this investigation. Used program applied ANSYS F.E.M code based on finite element method

• Computers and Concrete
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• v.14 no.3
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• pp.211-231
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• 2014

Prestressed hollow-core slabs (HCS) are widely used for modern lightweight precast floor structures because they are cost-efficient by reducing materials, and have excellent flexural strength and stiffness by using prestressing tendons, compared to reinforced concrete (RC) floor system. According to the recently revised ACI318-08, the web-shear capacity of HCS members exceeding 315 mm in depth without the minimum shear reinforcement should be reduced by half. It is, however, difficult to provide shear reinforcement in HCS members produced by the extrusion method due to their unique concrete casting methods, and thus, their shear design is significantly affected by the minimum shear reinforcement provision in ACI318-08. In this study, a large number of shear test data on HCS members has been collected and analyzed to examine their web-shear capacity with consideration on the minimum shear reinforcement requirement in ACI318-08. The analysis results indicates that the minimum shear reinforcement requirement for deep HCS members are too severe, and that the web-shear strength equation in ACI318-08 does not provide good estimation of shear strengths for HCS members. Thus, in this paper, a rational web-shear strength equation for HCS members was derived in a simple manner, which provides a consistent margin of safety on shear strength for the HCS members up to 500 mm deep. More shear test data would be required to apply the proposed shear strength equation for the HCS members over 500 mm in depth though.