• Journal of Korea Water Resources Association
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• v.43 no.3
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• pp.245-256
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• 2010

We study the basic theory and applicability of the WQUAL block in the FFC2Q model and the characteristics of non-point pollutant loads during the early stage of runoff. Study is also performed on selection of the values of the related parameters and their effect on the simulation results. FFC2Q simulation results are compared for verification with the measured data for three rainfall events in the Gunja Subbasin and found to be similar to the measured data in peak-flows, total runoff volumes, total loads, peak concentrations and times of peak concentration. This model thus shows results very close to those applying the SWMM and MOUSE models, even though it uses simplified input data. Related to rainfall distribution, under the condition of Huff 1st quartile distribution the pollutant loads occurred earlier than under other conditions, and in the early stage of rainfall the BOD and COD loads increased faster than the SS loads. The NPS loads were concentrated in the early stage of rainfall and finally reached total loads, so the rainfall after that could not contribute so much to the NPS loads.

• Restorative Dentistry and Endodontics
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• v.18 no.2
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• pp.291-316
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• 1993

Restorative procedures can lead to tooth fracture due to the relatively small amount of the remaining tooth structure. It is essential to prevent fractures by having a clear concept of the designs for cavity preparations. Among the several parameters in cavity designs, profound understanding of isthmus width factor would facilitate selection of the appropriate cavity preparation for a specific clinical situation. In this study, MO amalgam cavity were prepared on maxillary first premolar and filled with amalgam. Three dimensional, model with 1365 8-node brick elements was made by serial photographic method. In this model, isthmus was varied in width at 1/4, 1/3, 1/2 and 2/3 of intercuspal width and material properties were given for three element groups, i.e., enamel, dentin and amalgam. A load of 500 N was applied vertically on amalgam and enamel. In case of enamel loading, 2 model (with and without amalgam) was compared to consider the possibility of play at the interface between tooth material and amalgam. These models were analyzed with three dimensional finite element method. The results were as follows: 1. The stress was concentrated on the facio-pulpal line angle and distal marginal ridge of the cavity. 2. With the increase of the isthmus width, the stress spread around the facio-pulpal line angle and the area of stress concentration moved toward the proximal box. 3. In case of narrow isthmus width, the initiation point of crack would be in the area of isthmus corner of the cavity, and with the increase of the isthmus width, it would move toward the proximal box and at the same time the possibility of crack increase at the distal marginal ridge. 4. The direction of crack progressed outward and downward from the facio-pulpal line angle, and with the increase of the isthmus width, it approximated vertical direction. At the marginal ridge, it occurred in vertical direction. 5. It would be favorable to make the isthmus width narrower than a third of the intercuspal width, and to cover the cusp if isthmus width were wider than half of the intercuspal width. 6. It is necessary to apply the possibility of play to the finite element analysis.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.39-48
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• 2011

The present investigation evaluates the flexural behavior of pre-tensioned lightweight concrete beams under two-point symmetrical concentrated loads according to the variation of the partial prestressing ratio and the effective prestress of prestressing strands. The designed compressive strength of the lightweight concrete with a dry density of 1,770 $kg/m^3$ was 35 MPa. The deformed bar with a yield strength of 383 MPa and three-wire mono-strands with tensile strength of 2,040 MPa were used for longitudinal tensile reinforcement and prestressing steel reinforcement, respectively. According to the test results, the flexural capacity of pre-tensioned lightweight concrete beams increased with the increase of the partial prestressing ratio and was marginally influenced by the effective prestress of strands. With the same reinforcing index, the normalized flexural capacity of pre-tensioned lightweight concrete beams was similar to that of pre-tensioned normal-weight concrete beams tested by Harajli and Naaman and Bennett. On the other hand, the displacement ductility ratio of pre-tensioned lightweight concrete beams increased with the decrease of the partial prestressing ratio and with the increase of the effective prestress of strands. The load-displacement relationship of pre-tensioned lightweight concrete beam specimens can be suitably predicted by the developed non-linear two-dimensional analysis procedure. In addition, the flexural cracking moment and flexural capacity of pre-tensioned lightweight concrete beams can be conservatively evaluated using the elasticity theorem and the approach specified in ACI 318-08, respectively.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.7 no.2
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• pp.437-444
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• 2017

Stress concentrations around discontinuities, such as a hole in cross section of a structural member, have great importance because the most materials failure around the region may be occurred. Stress on the point applied by concentrated load reaches much larger value than the average stress in structural member. In this paper, stress analysis was performed for the plate with a partial through-hole to find the difference of the principal stress distribution. The difference between maximum principal stress and minimum principal stress in photoelasticity is equal to the value obtained by multiplying the isochromatic fringe order by the fringe constant of the material divided by the distance through which the light passes, that is, the thickness of the specimen. Since the difference of principal stress is proportional to the photoelastic fringe order, the distribution of the principal stress difference by the finite element analysis can be compared with the photoelasticity experimental result. ANSYS Workbench, that is the finite element software, is used to compute the differences of principal stresses at the specific points on the measured lines. The computation values obtained by ANSYS are compared with the experimental measurements by photoelasticity, and two results are comparable to each other. In addition, the stress concentration factor is obtained using the stress distribution analyzed from the variation of hole depth. Stress concentration factor is increasing, as the depth of hole increase.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.4
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• pp.325-334
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• 2008

Statement of problem & Purpose: The purpose of this study was to investigate the effect of a mouth guard material properties on the skull and brain when they were under impact loads on mandible. Material and methods: Two customized mouth protectors having different material propeerst ieach other were made for a female Korean who had no history of brain trauma, no cerebral diseases, nomal occlusion and natural dentition. The 3D finite element model of human skull and brain scanned by means of computed tomography was constructed. The FEM model of head was composed of 407,825 elements and 82,138 nodes, including skull, brain, maxilla, mandible, articular disc, teeth and mouth guard. The stress concentrations on maxillary teeth, maxilla and skull with two mouth guards were evaluated under oblique impact load of 800N onto mandibular 3 loading points for 0.1sec. And the brain relative displacement was compared in two different mouth guard materials under same condition. Result and Conclusion: The results were as follows; 1. In comparison of von Mises stress on maxillary teeth, a soft mouth guard material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 2. In comparison of von Mises stress on maxilla and skull, A soft mouth protector material had significantly lower stress values on measuring point than a hard mouth protector materials (P < .05). 3. For impact loads on mandible, there were more stress concentrated area on maxilla and skull with hard mouth guard than soft with mouth protector. 4. For impact loads on mandible, brain relative displacement had little relation with mouth guard material properties. In results of this study, soft mouth guard materials were superior to hard mouth guard materials for mandible impact loads for prevention of sports injuries. Although the results of this study were not enough to figure out the roles of needed mouth guard material properties for a human head, we got some knowledge of the pattern about stress concentration and distribution on maxilla and skull for impact loads with soft or hard mouth protector. More studies are needed to substantiate the relationship between the mouth guard materials and sports injuries.