Journal of the Korean Society of Marine Environment & Safety
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v.28
no.2
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pp.377-384
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2022
Vortex-induced vibration (VIV) occurs owing to the vortex generated from the back side of the appendages of ships and submarines during operation. Recently, the importance of high-order modes (HOMs) vibration and fatigue failure has become increasingly emphasized by increasing the speed of ships and the size of structures. In addition, predicting the vibration of HOMs is significantly necessary as the VIV becomes stronger in the fast flow speed condition than in the low flow speed condition. This study introduces a methodology according to HOMs hybrid Fluid Structure Interaction (FSI) for predicting the HOMs VIV on the hydrofoils. The HOMs FSI system is verified by comparing the VIV results from the FSI simulation with the experimental results. Finally, the effectiveness of the HOMs FSI is determined by applying the maximum von-Mises stress obtained from the VIV on the hydrofoil to the S-N curve released from Det Norske Veritas (DNV). VIV results from the HOMs FSI include the lock-in characteristics as well as a significant increase of more than 10 times compared with that of low-order modes (LOMs) FSI. In the future works, advanced studies will be required for improving cantilever boundary conditions and the shape of hydrofoils.
Journal of Korea Entertainment Industry Association
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v.15
no.3
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pp.183-192
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2021
This study was purposed to explore the learning culture through the related literature and research review in Jewish Havruta which has interaction, critical reflection, and the driving force creating a better world. The prior researches on Havruta mainly tend to as ways to increase learners' interest in learning and studies as curriculum or teaching methods such as creativity, understanding, and problem-solving skills. However, Havruta is not just method to study subjects, but rather a process of developing thinking through dialogue and discussion. Therefore, Havruta's essential meaning as a lifelong learning should be explored. Studies showed that Jews embody the thinking process from interpreting, analyzing, setting up logic, questioning, discussing, and debating Talmud with others anytime, anywhere, and anyone throughout their learning culture. It develops basic skills for life, forms an integrated personality in relationships with others, and continuously conducts lifelong learning to shape one's own beings. Therefore, lifelong learning culture would be sharing information that one has in the process of discussion through dialogue between two or more people, and supporting and encouraging the other's failure or fear rather than attacking them. The embodiment of thinking process in which people teach and learn eachother, accept the difference, and expand thought would be significant foundation to create lifelong learning culture.
Objectives This study was designed to evaluate the healing effect of Cordyceps Militaris (CM) on collagen II-induced arthritis rats. Methods Sprague-Dawley rats were randomly divided into 6 groups (normal, control, positive control, CM with low/medium/high dosage each). Type II collagen mixed with complete Freund's adjuvant (with 1:1 v/v) was injected subcutaneously, and the mixture was injected in a same manner one week after the first injection to boost arthritis. Arthritis index, paw thickness and von Frey test were conducted to observe physical changes. hematoxylin and eosin (H&E) staining was performed to observe knee cartilage. The levels of messenger RNA (mRNA) expressions of interleukin (IL)-1𝛽, IL-6, tumor necrosis factor-alpha (TNF-𝛼) in spleen were assessed by real-time polymerase chain reaction. Results Rheumatoid arthritis is an autoimmune disease that occurs on multiple joints and can lead to temporary shape change of bones or organ failure in severe cases. Here, we aimed to determine the effect of CM extract on rheumatoid arthritis by measuring paw thickness, arthritis index, conducting von Frey test and H&E staining, and evaluating the level of IL-1𝛽, IL-6, TNF-𝛼. As a result, paw thickness, arthritis index significantly decreased in low concentration group, hind leg became less sensitive in all expermental groups. Also, histological analysis showed that the damage of knee cartilage was prevented in all experimental groups. The level of mRNA of IL-1𝛽, IL-6, and TNF-𝛼 in spleen was analyzed to decide the effectiveness of CM extract. IL-1𝛽 did not show significant change, but IL-6 and TNF-𝛼 showed significant decrease in at least one of the experimental groups. Conclusions CM showed protective effect on knee tissue destruction and improved the physical conditions of the leg involving arthritis. Also, it showed that CM has anti-inflammatory effect on specific cytokines inducing rheumatoid arthritis. In conclusion, this study demonstrated that the therapeutic potential of CM for the treatment rheumatoid arthritis, and set the foundation for the further studies.
Kim, Uiseok;Kim, Junghoon;Kim, Jiyoon;Min, Byungchan;Choi, Hangseok
Journal of the Korean GEO-environmental Society
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v.22
no.12
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pp.5-13
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2021
Expandable steel pipe piles have been developed to ensure stability and reduce construction costs during underground floor remodeling and extension work. Expandable steel pipe piles are more economical and stable than micropiles. Extensible steel pipe pile is a method of improving the performance of steel pipes by expanding steel pipes underground. In this paper, the changes in buckling strength according to the shape of steel pipes in an extended steel pipe pile were identified, a numerical analysis model was developed to determine the expended part effect of bumps due to steel pipe expansion, and the optimal steel pipe expansion was calculated through material tests. The larger the expansion diameter of the steel pipe and the greater the number of expanded part, the greater the buckling strength. Numerical results showed that the number of expanded part has a greater effect on buckling strength than the expansion rate. When the expansion rate is more than 1.2 times, it can be seen that as the number of expanded part increases, the effect of increasing buckling strength increases significantly. It was also noted that the expanded part effect of the bumps occur significantly when the extension angle is less than 45° and the expansion rate is 1.3 times higher. When the steel pipe is failure, the expanded rate is 20 to 32%, averaging 25.4%. Through the material test, it was analyzed that it is desirable to limit the maximum expansion rate for performing steel pipes to 16%.
In order to investigate the stabilizing effect of nails against sliding, a series of model tests were carried out. The apparatus of model test was designed to perform the model test of soil slope reinforced by nails. The instrumentation system was used to measure the deflection behavior of nails during slope failure. As a result of model tests, the quantity and the occurred position of the maximum bending stress are changed according to the area ratio and the inclination angles of nails. The maximum stabilizing effect against sliding of nails is presented at 0.7$\%$ of the area ratio because the biggest maximum bending stress occurs at this time. But, the stabilizing effect of nails decreases with more than 0.7$\%$ of the area ratio. In the same condition of the area ratio, the stabilizing effect of nails is excellent at -10$^{circ}$ of the inclination angles of nails. The sliding surface can be predicted on the basis of the position of the maximum bending stress in each nails. The shape and depth of sliding surface are changed according to the area ratio and the inclination angles of nails.
Journal of Korean Tunnelling and Underground Space Association
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v.12
no.1
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pp.1-14
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2010
Until now, the evaluation method of spalling depth using Martin et al. (1999)'s linear regression relations has long been known applicable. However, it is not likely that the proposed equation is applicable to the openings other than circular type and mostly overpredict the spalling depth in comparison with actual spalling cases. Moreover, the evaluation method to estimate the spalling width has not been presented yet; it is essential to evaluate the spalling width in addition to the spalling depth, because the shape of the spalled region influences the choice of suitable rock reinforcement. In this study, linear regression equations, in which normalized spalling depth ($d_f/W_D$) and normalized spalling width ($w_f/W_D$) are functions of three spalling evaluation indices, ${\sigma}_1/{\sigma}_c,\;D_{is}(={\sigma}_{max}/{\sigma}_c)$ and ${\sigma}_{dev}/{\sigma}_{cm}$, are established based on in-situ spalling observations and CWFS simulation results. Confidence intervals of 95% using the statistical inference theory are used in verifying the reliability of linear regression equations. Spalling depth ($d_f$) and spalling width ($w_f$) predicted from the proposed linear regression relations, which take three spalling evaluation indices into account, showed reasonable match with in-situ observations by adopting weighting factors considering the degree of variance of linear regression relations.
Adhesive bonding is currently widely used in many industrial fields, particularly in the aeronautics sector. Despite its advantages over mechanical joints such as riveting and welding, adhesive bonding is mostly used for secondary structures due to its low peel strength; especially if it is simultaneously exposed to temperature and humidity; and often presence of bonding defects. In fact, during joint preparation, several types of defects can be introduced into the adhesive layer such as air bubbles, cavities, or cracks, which induce stress concentrations potentially leading to premature failure. Indeed, the presence of defects in the adhesive joint has a significant effect on adhesive stresses, which emphasizes the need for a good surface treatment. The research in this field is aimed at minimizing the stresses in the adhesive joint at its free edges by geometric modifications of the ovelapping part and/or by changing the nature of the substrates. In this study, the finite element method is used to describe the mechanical behavior of bonded joints. Thus, a three-dimensional model is made to analyze the effect of defects in the adhesive joint at areas of high stress concentrations. The analysis consists of estimating the different stresses in an adhesive joint between two 2024-T3 aluminum plates. Two types of single lap joints(SLJ) were analyzed: a standard SLJ and another modified by removing 0.2 mm of material from the thickness of one plate along the overlap length, taking into account several factors such as the applied load, shape, size and position of the defect. The obtained results clearly show that the presence of a bonding defect significantly affects stresses in the adhesive joint, which become important if the joint is subjected to a higher applied load. On the other hand, the geometric modification made to the plate considerably reduces the various stresses in the adhesive joint even in the presence of a bonding defect.
Purpose : We sought to determine the early change of ventricular geometry and function after concomitant surgeries of modified Dor procedure and mitral valve annuloplasty by using magnetic resonance imaging. Materials and Methods : We enrolled 21 patients with dilated heart failure who underwent modified Dor procedure (n=8), mitral valve annuloplasty (n=6), or both surgeries (n=7). Cine MRI was used to assess left ventricular dimensions and function before and after surgery. We measured the left ventricular end-diastolic and end-systolic volumes and the dimensions of the left ventricular long-axis and short-axis. Left ventricular stroke volume, ejection fraction, and sphericity index were calculated from these measurements. These parameters were analyzed and compared between three different surgery groups to explain the combined effect of the concomitant surgeries. Results : MRI was performed within average $12\;{\pm}\;15$ days (range 1-58 days) before and $38\;{\pm}\;50$ days (range 7- 231 days) after the surgery. The patients who underwent concomitant surgeries had more profound enlargement of left ventricle and decreased contractility prior to surgery than those in the patients who underwent single surgical procedure. Left ventricular end-diastolic volume and endsystolic volume significantly decreased in all patients regardless of surgery type after surgery. Ejection fraction significantly increased only in the patients who got modified Dor procedure without mitral valve annuloplasty (25.4% to 40.7%). Sphericity index increased in patients with modified Dor procedure but decreased in patients with mitral valve annuloplasty (0.65 to 0.78 vs. 0.75 to 0.65). In the patients who underwent concomitant surgeries showed no significant change in sphericity index after surgery. Conclusion : The early change of the left ventricular geometry and function after the concomitant surgeries with modified Dor procedure and mitral valve annuloplasty in patients with dilated heart failure includes a marked reduction in left ventricular volume and in stroke volume. The shape of the left ventricle does not change because the effect of sphericity index decrease from mitral valve annuloplasty is counteracted by the effect of sphericity index increase from modified Dor procedure. Improvement of left ventricular ejection fraction is not the early change after the concomitant surgeries.
Flowable composite resin has lower filler content, increased flow, and lower modules of elasticity. It is suggested that flowable composite resin can be bonded to the tooth structure intimately and absorb or dissipate the stress. Therefore, it may be advantageous to use flowable composite resin for the base material of class II restoration and for the class V restoraton. The purpose of this study was to evaluate the microleakage and shear bond strength of four flowable composite resins (Aeliteflo, Flow-It, Revolution, Ultraseal XT Plus) compared to Z100 using Scotchbond Multi Purpose dentin bonding system. To evaluate the microleakage, notch-shaped class V cavities were prepared on buccal and lingual surfaces of 80 extracted human premolars and molars on cementum margin. The teeth were randomly divided into non-thermocycling group (group 1) and thermocycling group (group 2) of 40 teeth each. The experimental teeth of each group were randomly divided onto five subgroups of eight samples (sixteen surfaces). The Scotchbond Multi-Purpose and composite resin were applied for each group following the manufacturer's instructions. the teeth of group 2 were thermocycled five hundred times between 5$^{\circ}C$ and 55$^{\circ}C$. The teeth of group 2 were placed in 2% methylene blue dye for 24 hours, then rinsed with tab water. The specimens were embedded in clear resin, and sectioned longitudinally with a diamond saw. The dye penetration on each of the specimen were observed with a stereomicioscope at $\times$20 magnification. To evaluate the shear bond strength, 60 teeth were divided into five groups of twelve teeth each. The experimental teeth were ground horizontally below the dentinoenamel junction, so that no enamel remained. After applying Scotchbond Multi-Purpose on the dentin surface, composite resin was applied in the shape of cylinder. The cylinder was 4mm in diameter and 2mm in thickness. Shear bond strength was measured using Instron with a cross-head speed of 0.5mm/min. After shear bond strength measurement, mode of failure was evaluated with a stereomicroscope at $\times$30 magnification. All data were statistically analyzed by One Way ANOVA and Student-Newman-Keuls method. The correlation between microleakage and shear bond strength was analyzed by linear regression. The results of this study were as follows ; 1. In non-thermocycling group, the leakage value of Z100 was significantly lower than those of flowable composite resins at the enamel and dentin margin, margin, except that Revolution showed the lower leakage value than that of Z100 at the dentin margin (p<0.05). 2. In thermocycling group, the leakage values of Z100 and Ultraseal XT Plus were lower than those of other subgroup at the enamel and dentin margin, except that Flow-It showed the lower leakage value than that of Ultraseal XT Plus at the dentin margin (p<0.05). 3. The leakage value of Z100 and Ultraseal XT Plus in thermocycling group were not higher than that in non-thermocycling group at the enamel margin. The leakage value of Z100 in thermocycling group was not higher than that in non-thermocycling group at the dentin margin (p<0.05). 4. As for the shear bond strength measurement, there were no statistically significant differences among groups (p<0.05). The shear bond strengths given in descending order were as follows: Z100(16.81$\pm$2.98 MPa), Flow-It(14.8$\pm$4.43 MPa), Aeliteflo(14.34$\pm$3.69 MPa), Revolution(13.46$\pm$4.23 MPa), Ultraseal XT Plus(12.83$\pm$3.16 MPa). 5. Failure modes of all specimens were adhesive failures. 6. There was no correlation between microleakage and shear bond strength.
Kim, Youngho;Kim, Hoyeon;Kim, Yeonsam;You, Seung-Kyong;Han, Jung-Geun
Journal of the Korean Geosynthetics Society
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v.16
no.4
/
pp.231-240
/
2017
Recently, there have been frequent occurrences of ground sink in the urban area, which have resulted in human and material damage and are accompanied by economic losses. This is caused by artificial factors such as soil loss, poor compaction, horizontal excavation due to the breakage of the aged sewage pipe, and lack of water proof at vertical excavation. The ground sink can be prevented by preliminary restoration and reinforcement through exploration, but it can be considered that it is not suitable for urgent restoration by the existing method. In this study, a model experiment was carried out to simulate the in-ground cavities caused by groundwater flow for developing non-excavation urgent restoration in underground cavity and the range of the relaxation zone was estimated by detecting the around the cavity using a relaxation zone detector. In addition, disturbance region and relaxation region were separated by injecting gypsum into cavity formed in simulated ground. The shape of the underground cavity due to the groundwater flow was similar to that of the failure mode III formed in the dense relative density ground due to water pipe breakage in the previous study. It was confirmed that the relaxed region detected using the relaxation zone detector is formed in an arch shape in the cavity top. The length ratio of the relaxation region to the disturbance region in the upper part of the cavity center is 2: 1, and it can be distinguished by the difference in the decrease of the shear resistance against the external force. In other words, it was confirmed that the secondary damage should not occur in consideration of the expandability of the material used as the injecting material in the pre-repair and reinforcement, and various ground deformation states will be additionally performed through additional experiments.
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