• Tunnel and Underground Space
• /
• v.24 no.2
• /
• pp.155-165
• /
• 2014

Multiple thermal energy storage (TES) caverns can be used for storing thermal energy on a large scale and for a high-aspect-ratio heat storage design to provide good thermal performance. It may also be necessary to consider the use of multiple caverns with a reduced length when a single, long tunnel-shaped cavern is not suitable for connection to aboveground heat production and injection equipments. When using multiple TES caverns, the separation distance between the caverns is one of the significant factors that should be considered in the design of storage space, and the optimal separation distance should be determined based on a quantitative stability criterion. In this paper, we described a numerical approach for determining the optimal separation distance between multiple caverns for large-scale TES utilization. For reliable stability evaluation of multiple caverns, we employed a probabilistic method which can quantitatively take into account the uncertainty of input parameters by probability distributions, unlike conventional deterministic approaches. The present approach was applied to the design of a conceptual TES model to store hot water for district heating. The probabilistic stability results of this application demonstrated that the approach in our work can be effectively used as a decision-making tool to determine the optimal separation distance between multiple caverns. In addition, the probabilistic results were compared to those obtained through a deterministic analysis, and the comparison results suggested that care should taken in selecting the acceptable level of stability when using deterministic approaches.

• Journal of Korean Society of Steel Construction
• /
• v.29 no.1
• /
• pp.81-88
• /
• 2017

Residual stress is defined as stress that already exists on a structural member from the effects of welding and plastic deformation before the application of loading. Due to such residual stress, welded H-section compression members under centroidal compression load can undergo buckling and failure for strength values smaller than the predicted buckling load and specified compressive strength. Therefore, this study was carried out to evaluate the effect of residual stress from welding on the determination of the buckling load and specified compressive strength of the H-section compression member according to the column length variation. A three-dimensional nonlinear finite element analysis was performed for the H-section compression member where the welded joint was fillet welded by applying heat inputs of 3.1kJ/mm and 3.6kJ/mm using the SAW welding method.

• Radiation Oncology Journal
• /
• v.30 no.4
• /
• pp.158-164
• /
• 2012

Purpose: To evaluated the patterns of failure, survival rate, treatment-related toxicity and prognostic factors in postoperative radiotherapy of patients with ependymoma. Materials and Methods: Thirty patients who underwent surgery and postoperative radiotherapy for ependymoma between the period of June 1994 and June 2008 were reviewed retrospectively. The age of patients ranged from 21 months to 66 years (median, 19 years). Seventeen patients had grade II ependymoma, and 13 had grade III anaplastic ependymoma according to the World Health Organization grading system. The postoperative irradiation was performed with 4 or 6 MV photon beam with median dose of 52.8 Gy (range, 45 to 63 Gy), and radiation field including 2 cm beyond the preoperative tumor volume. Median follow-up period was 51 months (range, 12 to 172 months). Results: Fourteen out of 30 (46.7%) patients experienced recurrence, and 12 of those died. Among those 14 patients who experienced recurrence, 11 were in-field and 3 were out-of-field recurrence. The 5-year overall survival (OS) and progression-free survival (PFS) rates were 66.7% and 56.1%, respectively. On univariate analysis, tumor grade was a statistically significant prognostic factor for OS and PFS. There were two complications after surgery and postoperative radiotherapy, including short stature and facial palsy on the left side. Conclusion: We observed good survival rates, and histologic grade was a prognostic factor affecting the OS and PFS. Almost all recurrence occurred in primary tumor site, thus we suggest further evaluation on intensity-modulated radiotherapy or stereotatic radiosurgery for high-risk patients such as who have anaplastic ependymoma.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.26 no.4
• /
• pp.412-418
• /
• 2020

Generally, the propeller shaft that constitutes the ship shaft system has different patterns of behavior due to the ef ects of engine power, propeller load and eccentric thrust, which increases the risk of bearing failure by causing local load variations. To prevent this, different studies of the propulsion shaft system have been conducted focused the relative inclination angle and oil film retention between the shaft and the support bearing, mainly with respect to the Rules for the Classification of Steel Ships. However, in order to secure the stability of the propulsion shaft via a more detailed evaluation, it is necessary to consider dynamic conditions, including the transient state due to sudden change in the stern wakefield. In this context, a 50,000 DWT vessel was analyzed using the strain gauge method, and the effects of propeller shaft movement were analyzed on the starboard rudder turn which is a typical transient state during normal continuous rate(NCR) operation in ballast draught condition. Analysis results confirm that the changed propeller eccentric thrust acts as a force that temporarily pushes down the shaft to increase the local load of the stern tube bearing and negatively affects the stability of the shaft system.

• Journal of the Microelectronics and Packaging Society
• /
• v.18 no.2
• /
• pp.49-55
• /
• 2011

The failure of electronic instruments is mostly caused by heat and shock. This shock causes the crack initiation at the solder joint interface of PCB component which is closely related with the formation of intermetallic compound(IMC). The Ag content in Pb-free Sn-xAg-0.5Cu solder alloy used in this study was 1.0, 1.2 and 3.0 wt.%, respectively. After soldering with PCB component, isothermal aging was performed to 1000 hrs. The growth of IMC layer was observed during isothermal aging. The drop impact property of solder joint was evaluated by impact bending test method. The solder joint made with the solder containing lower Ag content showed better impact bending property compared with that with higher Ag content. On the contrary to this result, the solder joint made with solder containing higher Ag content showed better impact bending property after aging. It should be caused by the formation of fine $Ag_3Sn$, which relieved the impact. It showed consequently the different effect of fine $Ag_3Sn$ and coarse $Cu_6Sn_5$ particles formed in the IMC layer on the impact bending property.

• Journal of the Korean Geotechnical Society
• /
• v.30 no.6
• /
• pp.5-21
• /
• 2014

It has been pointed out that the collapses of unsaturated road embankments caused by earthquake are attributed to high water content caused by the seepage of the underground water and/or the rainfall infiltration. Hence, it is important to study influences of water content on the dynamic stability and deformation mode of unsaturated road embankments for development of a proper design scheme including an effective reinforcement to prevent severe damage. This study demonstrates dynamic centrifugal model tests with different water contents to investigate the effect of water content on deformation and failure behaviors of unsaturated road embankments. Based on the measurement of displacement, the pore water pressure and the acceleration during dynamic loading, dynamic behavior of the unsaturated road embankments with about optimum water content and the higher water content than the optimum one have been examined. In addition, an image analysis has revealed the displacement field and the distributions of strains in the road embankment, by which deformation mode of the road embankment with higher water content has been clarified. It has been confirmed that in the case of higher water content the settlement of the crown is large mainly owing to the volume compression underneath the crown, while the small confining pressure at the toe and near the slope surface induces large shear deformation with volume expansion.

• The Journal of Korean Academy of Prosthodontics
• /
• v.58 no.4
• /
• pp.300-305
• /
• 2020

Purpose: The purpose of this study is to compare the shear bond strength of 3D printing denture base resin according to surface treatment of artificial teeth. Materials and methods: 3D printing denture base resin was fabricated as specimens using 3D printer. The experimental group divided the surface treatment of artificial teeth into five groups according to the application of sandblasting and primer (n=10). Shear bond strengths between denture base and artificial teeth were measured by universal testing machine. All measurements were analyzed by one-way ANOVA and Turkey test (α=.05). Fracture mode of each specimen was analyzed. Microscopic evaluation was conducted by using a scanning electron microscope. Results: Unsurfaced treated group represented the lowest value. The primer groups had significantly higher result values (P<.05). Most specimens of the primer groups had cohesive failure. Conclusion: In 3D printing denture base resin group, mechanical and chemical surface treatment of artificial teeth has increased the shear bond strength. Therefore, if dentures are produced using 3D printing, proper mechanical and chemical treatment of artificial teeth is necessary for adhesion of dentures and artificial teeth.

• Journal of The Korean Association For Science Education
• /
• v.24 no.3
• /
• pp.468-480
• /
• 2004

It has been criticized that there are discrepancy between 'general statements' of the curriculum and subject-matter curricula. The possible reasons for this are as follows: The developers of the general statements were educational curriculum specialists. These specialists were not good enough to develop general statements and guidelines of subject matter curricula reflecting the characteristics of science contents, to examine developed science curriculum, and to give feedback to science curriculum developers. Under the present curriculum developing system where curriculum is developed in ten months or less by the research team commissioned unpredictably and imminently, it might be difficult to develop valid and precise science curriculum reflecting the purport of the general statements and teachers' needs. The inadequacy of these curriculum development processes resulted in (1) inconsistent statement about the school year to be applied to differentiated curriculum, (2) abstract and ambiguous stating about the characteristics, teaching-learning and assessment guidelines of enrichment activities, and (3) failure to reduce science contents to a reasonable level. Therefore curriculum development centers should be designated in advance to do basic research at ordinary times, and organized into a cooperative system among them. Two years or more of developing time and wider participation of scientists are recommended to develop more valid and precise science curriculum. In addition, commentaries on science curriculum should be published before textbook writing begins.

• Magazine of the Korea Concrete Institute
• /
• v.9 no.4
• /
• pp.167-176
• /
• 1997

The current study is a part of series of research about the evaluation method of the unbonded tendon stress in prestressed concrete member at flexural failure. As the first part. previous design equations were examined in oder to find whether any modifications may be needed. A total of 167 experimental results tested for more than 40 years were gathered to build D/B and then previous proposed and codified equations were evaluated with the experimental relsults. The ACI Code equation and Naaman, Harajli, and Chakrabarti's equations were chosen for the purpose of examination. Then, the followings were obtained from the analytical examination. It is desirable to compute the tendon stress with the member analysis method instead of the sectional analysis method which has been used in the current ACI Code. The tendon stress may also be influenced significantly by the amount of ordinary bonded reinforcements and the loading types. And the current ACI Code overestimated the effect of span/depth ratio. As results, it was concluded that the revision of the ACi Code equation should be considered positively. Then, a new design has to be proposed with the reasonable and comprehensive investigation about influential factors on the tendon stress variation.

• Journal of the Korea Concrete Institute
• /
• v.27 no.3
• /
• pp.207-214
• /
• 2015

This study examined the feasibility of wire ropes as lateral reinforcement at the boundary element of heavyweight concrete shear walls. The spacing of the wire ropes varied from 60 mm to 120 mm at an interval of 30 mm, which produces the volumetric index of the lateral reinforcement of 0.126~0.234. The wire ropes were applied as a external hoop and/or internal cross-tie. Five shear wall specimens were tested to failure under constant axial load and cyclic lateral loads. Test results showed that with the increase of the volumetric index of the lateral reinforcement, the ductility of shear walls tended to increase, whereas the variation of flexural capacity of walls was minimal. The flexural capacity of shear walls tested was slightly higher than predictions determined from ACI 318-11 procedure. The displacement ductility ratio of shear walls with wire ropes was higher than that of shear wall with the conventional mild bar at the same the volumetric index of the lateral reinforcement. In particular, the shear walls with wire rope index of 0.233 achieved the curvature ductility ratio of more than 16 required for high-ductility design.