• Tunnel and Underground Space
• /
• v.14 no.3
• /
• pp.229-240
• /
• 2004

Coastal aquifers may serve as major sources fur freshwater. In many coastal aquifers, intrusion of seawater has become one of the major constraints imposed on groundwater utilization. The management of groundwater in coastal acquifers means making decision as to the pumping rate and the spatial distribution of wells. Several numerical techniques for flow and solute transport simulation can provide the means to achieve this goal. As a basic study to predict the intrusion of seawater in coastal phreatic aquifers, the coupled flow and solute transport analysis was conducted by use of the 3-D finite element code, SWICHA. In order to understand how the location and the shape of freshwater-seawater transition zone were affected by the boundary conditions and hydrogeologic variables, parametric study was carried out.

• Restorative Dentistry and Endodontics
• /
• v.36 no.6
• /
• pp.515-520
• /
• 2011

One of the most challenging task in closing anterior diastema is avoiding "black triangle" between the teeth. This paper reports a case that the closure of diastema in anterior teeth could be successfully accomplished using direct adhesive restorations and gingival recontouring. The traditional technique using Mylar strip was modified to increase the emergence profile with natural contours at the gingival-tooth interface. Mylar strip was extended out of the sulcus by approximately 1 mm high from the gingival margin, and a small cotton pellet was used to provide the emergence contour. This modified approach is acceptable for the clinical situation.

• Geotechnical Engineering
• /
• v.13 no.3
• /
• pp.5-20
• /
• 1997

A governing equation of uncoupled three dimensional finite strain theory of consolidation is presented. This equation is suitable for relatively thick layers, possessing large strain, non-linear material property, and variable permeability. A special numerical solution procedure has to be adopted for the finite difference scheme because the solution is not stable in using Forward-Time Centered-Space (FTCS) method and the governing equation is highly non-linear. The solution is capable of predicting settlement with respect to time. The results predicted by the developed method of analysis have been compared with those of experimental tests on different types of highly compressible soils with vertical wick drain. The uncoupled three dimensional finite strain theory of consolidation appears to predict settlement behavior well. A detailed comparison shows good agreement in terms of total settlement, and reasonable agreement with respect to time.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.10
• /
• pp.1695-1702
• /
• 2003

Fatigue crack initiation around a hole subjected to biaxial fatigue loads with a phase difference was investigated. Axial and torsional biaxial fatigue loads with different phase differences and biaxiality of 1/√3 were applied to thin-walled tubular specimens. Five phase differences of 0, 45, 90, 145 and 180 degrees were selected. Directions of the fatigue crack initiation around the hole were found to approach to the circumferential direction of the specimen with increment of the phase difference for fatigue tests with phase differences less than 90$^{\circ}$. Whereas directions for tests with phase differences greater than 90$^{\circ}$ got away from the circumferential direction and those were symmetric to the directions for tests with phase difference less than 90. . Furthermore, it was shown that the fatigue initiation life decreased with increment of phase difference for fatigue tests with phase differences less than 90$^{\circ}$, but it increased for tests with phase difference greater than 90$^{\circ}$. The crack initiation direction can be successfully explained by using the direction of the maximum tangential stress range obtained around the hole and at far-field.

• The Journal of Korean Academy of Prosthodontics
• /
• v.48 no.4
• /
• pp.273-279
• /
• 2010

Purpose: The purpose of this in vitro study was to compare the marginal adaptation of a ceramic-pressed-to-metal restoration with traditional metal-ceramic restoration. Materials and methods: Duplicating the prepared resin tooth, 20 metal dies were fabricated. Twenty metal copings of 2 groups which were metal ceramic restoration and pressed to metal restoration were fabricated. The marginal opening of each coping was measured with Microscope (BX 60M-36E $41D^{(R)}$: Olympus, Japan). After porcelain build-up, the marginal opening of metal ceramic restoration and pressed to metal restoration ($PoM^{(R)}$: Ivoclar vivadent., Liechtenstein) were also evaluated in the same method. The measurements were analyzed using Wilcoxon Signed Ranks test and Mann-Whitney U test. Results: Within the limits of this study, the results were as follows. 1. Metal-ceramic restorations in coping state ($64.93{\pm}12.48\;{\mu}m$) in compared with Metal ceramic restorations after porcelain build-up ($63.43{\pm}12.86\;{\mu}m$) had no significant difference in marginal adaptation. 2. Pressed-metal-ceramic restorations in coping state ($50.00{\pm}12.28\;{\mu}m$) in compared with Pressed metal ceramic restorations after porcelain build-up ($56.72{\pm}13.80\;{\mu}m$) had no significant difference in marginal adaptation. 3. Metal-ceramic restorations in compared Pressed-metal-ceramic restorations had no significant difference in marginal adaptation. Conclusion: Pressed-metal-ceramic restorations have the advantage of being technically less change through using of the lost-wax technique and this allows for the convenience of a full-contour ceramic wax-up as opposed to the more technique-sensitive layering method. Pressed-metal-ceramic restorations may be considered in clinic on the basis of the result of this study and the advantage of this system.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2021.06a
• /
• pp.27-27
• /
• 2021

세굴은 유체와 유사의 상호작용으로 발생하는 중요한 자연 현상 중 하나로, 구조 및 지반 붕괴, 홍수, 생태계 파괴 등의 문제를 야기할 수 있다. 이러한 세굴 현상을 예측하기 위해 많은 수치적 연구가 진행되어왔지만, 대부분의 연구가 기존 격자기반방법인 유한체적법 (FVM)과 개별요소법 (DEM)이 연성된 모델을 이용하였고, 이는 격자 의존도로 인한 정확도와 효율성의 문제점을 보였다. 해결책으로 입자기반 유체해석 방법인 약압축성 SPH (WCSPH)와 개별요소법의 결합모델을 이용한 모의가 연구되어 왔지만, 단순 밀도차를 활용한 유체해석방법이 압력의 불안정성을 야기하여 유사의 운동에도 영향을 주는 결과를 보였다. 또한, 개별요소법의 특성상 모의 입자의 크기를 실제 실험 입자의 크기와 동일하게 설정하면서 입자수가 지나치게 증가해 계산의 효율성이 현저히 낮아지게 되었고, 이로 인해 실제 자연 지형에 적용하는데 어려움을 보여주었다. 본 연구에서는 향상된 세굴 수치모의해석을 위해 반복법을 통해 안정적인 유체 압력을 계산하는 비압축성 SPH (ISPH)와 개별요소법을 연성한 ISPH-DEM 모델을 사용하였다. 또한, 계산속도 향상을 위해 하나의 입자가 다수의 작은 입자의 움직임을 대표하는 Coarse-grained 방법을 적용하여 기존 모델을 개선하였다. 개선된 모델을 NFLOW ISPH PURPLE 소프트웨어를 이용하여 세굴 현상을 수치 모의하였고 실험 결과와 검증을 진행한 결과, 세굴의 깊이, 너비, 형상 등을 비교하였을 때 약 10% 이내의 오차를 보였고, Coarse-grained 방법을 통한 입자 수 감소로 최소 13배 증가된 해석 속도를 보였다. 이를 통해 본 연구에서 제시된 모델이 실제 자연 지형에서의 적용가능성을 확인할 수 있었다.

• Journal of dental hygiene science
• /
• v.13 no.2
• /
• pp.135-141
• /
• 2013

One factor for successful prognosis of finished dental prosthesis is good marginal fit. The purpose of this study in vitro investigation was to compare the marginal fit of all-ceramic crown before and after porcelain veneering, to evaluate the influence of high temperature of the porcelain firing on the fit. For this experiment, model of abutment tooth of maxillary right central incisor was prepared. Ten working models were produced. Ten zirconia cores were made by dental computer aided design/computer aided manufacturing system. The marginal fit of specimens were examined using silicone replica technique. Silicone replicas were sectioned four times and were measured through a digital microscope (${\times}160$). Marginal fit is a distance connected between edge end part of specimen and abutment margin. Each specimens was measured twice, the first measurement was done prior to veneering porcelain firing, while the second measurement was done after the porcelain firing to evaluate this process. Statistical analyses were performed with paired t-test. $Mean{\pm}SD$ marginal fit was $60.8{\pm}14.2{\mu}m$ for zirconia core and $86.1{\pm}13.3{\mu}m$ for all-ceramic crown. They were statistically significant differences (p<0.001). But all specimens showed a marginal fit where the gap widths ranged within the clinical recommendation ($120{\mu}m$), all-ceramic crown production using the zirconia core was adequate.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.4
• /
• pp.2585-2592
• /
• 2015

The purpose of this study was to evaluate the shear bond strength between metal core fabricated by 3D printing and dental porcelain. Thirty metal cores were fabricated(cast 15ea, 3D printing 15ea). The porcelain for each group was builded to the metal core. Sample was loaded to shear force(crosshead speed 1mm/min) in a universal material testing machine. The fracture samples were analyzed failure aspect. The means were statistical analyzed using by Mann-whitney test(${\alpha}=0.05$). The period of experimental(metal cores fabrication, dental porcelain build up, data analysis, statistical analysis, failure aspect analysis and others) for this study took six months. The $mean{\pm}SDs$ of shear bond strength was $50.14{\pm}1.60MPa$ for the cast group, and $54.36{\pm}3.18MPa$ for the 3D printing group(p=0.035). The failure aspect showed mixed failure. As a results, metal cores fabricated by 3D printing method were clinically acceptable range.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.7
• /
• pp.1159-1169
• /
• 2003

This paper investigates the effects of T-stress and plastic hardening mismatch on the interfacial crack-tip stress field via finite element analyses. Plane strain elastic-plastic crack-tip fields are modeled with both MBL formulation and a full SEC specimen under pure bending. Modified Prandtl slip line fields illustrate the effects of T-stress on crack-tip constraint in homogeneous material. Compressive T-stress substantially reduces the interfacial crack-tip constraint, but increases the J-contribution by lower hardening material, J$\_$L/. For bimaterials with two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint in the lower hardening material and J$\_$L/. The fracture toughness for bimaterial joints would consequently be much lower than that of lower hardening homogeneous material. The implication of unbalanced J-integral in bimaterials is also discussed.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.120-126
• /
• 1991

An expanded scheme of a direct numerical solution method for solving the Navier-Stokes equation considering the modified boundary conditions for gas lubrication with ultra low clearance at high .LAMBDA. region is presented. Many examples are calculated by this scheme and their results are compared to the previous solutions using P$^{2}$H$^{[-992]}$ . This scheme has the advantages of fast calculation time and stable convergence in high .LAMBDA. region, and gives very good results in the case of fluid film thickness discontinuity.