• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1803-1806
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• 2007

The General roles of a spacer grid(SG) are providing a lateral and vertical support for fuel rods, promoting a mixing of coolant and keeping guide tubes straight so as not to impede a control rod insertion under any normal or accidental conditions. To evaluate the impact characteristics of a SG such as impact velocity, critical buckling strength and duration time, a few types of impact tests for SGs have been conducted. In a previous study, a new welding method, a through-welding method, was proposed to increase critical buckling strength of a SG without any design change or material change and was verified by impact tests with $7{\times}7$ partial SG specimens.In this paper, the effect of through-welding method in case of a $16{\times}16$ full-size SG is investigated by pendulum impact tests with $16{\times}16$ SG specimens. And the increase of critical buckling strength for full-size SGs is measured by comparison with impact results of spot-welded and through-welded SGs.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.11
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• pp.93-100
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• 2001

Brittle materials are very weak for impact because of typical characteristics which happen to be easily fractured with low fracture toughness and crack sensitivity. When brittle materials are subjected to impact due to small spheres, high contact pressure is occurred to impact surface and then local damage on specimen is developed, since there are little plastic deformations due to contact pressure compared to metals. This local damage is a dangerous factor which gives rise to final fracture of structures. In this research, the crack propagation process of soda lime glass by impact of small sphere is explained and the effects of the constraint conditions of impact spheres and materials for the material damage were studied by using soda-lime glass. that is the effects for the materials and sizes of impact ball, thickness of specimen and residual strength. Especially, this research has focused on the damage behavior of ring crack, cone crack and several kinds of cracks.

• Structural Engineering and Mechanics
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• v.51 no.3
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• pp.487-502
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• 2014

In buildings structures, the flexural stiffness reduction of beams and columns due to concrete cracking plays an important role in the nonlinear load-deformation response of reinforced concrete structures under service loads. Most Seismic Design Codes do not precise effective stiffness to be used in seismic analysis for structures of reinforced concrete elements, therefore uncracked section properties are usually considered in computing structural stiffness. But, uncracked stiffness will never be fully recovered during or after seismic response. In the present study, the effect of concrete cracking on the lateral response of structure has been taken into account. Totally 120 cases of 3 Dimensional Dynamic Analysis which considers the real and accidental torsional effects are performed using ETABS to determine the effective structural system across the height, which ensures the performance and the economic dimensions that achieve the saving in concrete and steel amounts thus achieve lower cost. The result findings exhibits that the dual system was the most efficient lateral load resisting system based on deflection criterion, as they yielded the least values of lateral displacements and inter-storey drifts. The shear wall system was the most economical lateral load resisting compared to moment resisting frame and dual system but they yielded the large values of lateral displacements in top storeys. Wall systems executes tremendous stiffness at the lower levels of the building, while moment frames typically restrain considerable deformations and provide significant energy dissipation under inelastic deformations at the upper levels. Cracking found to be more impact over moment resisting frames compared to the Shear wall systems. The behavior of various lateral load resisting systems with respect to time period, mode shapes, storey drift etc. are discussed in detail.

• Journal of the Korea institute for structural maintenance and inspection
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• v.1 no.2
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• pp.115-122
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• 1997

Although most bridge foundations are usually constructed by Caisson, terrain difficulties sometimes bring about constructing bridge foundations by Jacket piles. This study investigated the dynamic characteristics of Caisson and Jacket by testing the impact applied to actual bridge foundations. The test result showed that the damping ratio of the foundation constructed by Jacket and Caisson were measured 1-2% and 3-6%, respectively. Considering the lateral deflection measured by the impact test, the rigidity of foundations constructed by Jacket was assessed about 1/5 - 1/6 of those constructed by Caisson. It implies that designing bridge foundations should include and reflect the dynamic analysis of bridge foundation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.1
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• pp.93-103
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• 1997

Charpy V-notch impact tests were performed on the full-, half-and third-size specimens from two ferritic SA 508 Cl. 3 steels for nuclear pressure vessel. New normalization factors were proposed to predict the upper shelf energy(USE) and the ductile-brittle transition temperature(DBTT) of full-size specimens from the measured data on sub-size specimens. The factors for the USE and the DBTT are $(Bb^2/Kt); and; (Bb/R)^1/2/, $ respectively, where B the width, b the ligament size, $K_{t}$ the elastic stress concentration factor, and R the notch root radius. These correlations successfully estimated the USE and DBTT of the full-size specimens based on sub-size specimen data. In addition, the size effects were studied to develop the correlations among absorbed energy, lateral expansion(LE) and displacement. It was also found that the LE was able to be estimated from the displacement obtained by the instrumented impact test, and that the displacement would be used as a criterion for the toughness of the steels corresponding to change in their yield strength.h.

• Archives of Craniofacial Surgery
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• v.9 no.2
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• pp.62-66
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• 2008

Purpose: Although nasal fractures are often discussed as minor injuries but the incidence of post-traumatic nasal deformity remains high. For decrease the incidence of post-traumatic nasal deformity which require the guideline to optimize the management of acute nasal bone fracture. The aim of this study is analysis of post-traumatic nasal deformity according to Stranc classification. Method: We reviewed 310 patients with nasal bone fracture treated at our hospital from January of 2005 to December of 2006. Result: Post-traumatic complication were divided septal deviation, nasal bone deformity, temporary hyposmia and synechia. Nasal bone deformity include nasal bone deviation, hump, flat nose and minimal nasal bone irregularity. The incidence of total complication rate was 36.4%. The most common complication was nasal deformity(22.9%) followed by septal deviation(19.7%). The most common complication was septal deviation(20%) in frontal impact. The most common complication was nasal deformity(19.5%) in lateral impact. In frontal impact, the incidence of complication rate was plane II(68.8%) followed by plane I(29.9%) and plane III(16.7%). In lateral impact, the incidence of complication rate was plane II (78.8%) followed by plane III(61.5%) and plane I(42.7%). Conclusion: This result can be used to improve longterm results and to reduce the incidence of post-traumatic nasal deformity by predict complication of nasal bone fracture according to Stranc classification.

• Archives of Craniofacial Surgery
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• v.18 no.1
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• pp.25-29
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• 2017

Background: Many authors have evaluated the post-reduction result of nasal bone fracture through patient satisfaction or postoperative complications. However, these results are limited because they are subjective. The aim of this study was to correlate an objective operation result with patient satisfaction and postoperative complications according to the type of nasal bone fractures. Methods: Our study included 313 patients who had isolated nasal bone fractures and had undergone a closed reduction. Postoperative outcomes were evaluated objectively using computed tomographic (CT) images, while patient satisfaction was evaluated one month after the operation. The correlation of the operation result with patient satisfaction was then evaluated. Results: The correlation between the operation result and patient satisfaction was highest for the lateral impact group type I (LI) type of fracture and lowest for the comminuted fracture group (C) type of fracture. However, there were no statistically significant differences in correlation between the overall result and patient satisfaction by fracture type. The complication rate of lateral impact group type II (LII), C, and frontal impact group type I (FI) fractures were statistically significantly higher than that of frontal impact group type II (FII) and LI fractures. There were no statistically significant relationships between the prevalence of complications and septal fracture or deviation according to the fracture type. In the total group, however, there was a statistically significant difference in complication rate by septal fracture. Conclusion: We found that the CT outcomes correlated with patient satisfaction. The complication rate of LII, C, and FI fractures were statistically significantly higher than that of FII and LI fractures. Septal fracture/deviation increased the postoperative complication in the total group.

• Archives of Craniofacial Surgery
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• v.18 no.1
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• pp.30-36
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• 2017

Background: Nasal fractures have a tendency of resulting in structural or functional complications, and the results can vary according to the type of nasal bone fracture. The aim of this study was to evaluate the objective postoperative results according to the type of nasal bone fractures. Methods: We reviewed 313 patients who had a closed reduction of nasal bone fracture. The classification of nasal bone fracture by Stranc and Robertson was used to characterize the fracture type: frontal impact group type I (FI), frontal impact group type II (FII), lateral impact group type I (LI), lateral impact group type II (LII), and comminuted fracture group (C). For each patient, we tried to use the same axial image section of computed tomographic (CT) scans before and immediately after operation. Postoperative outcomes were classified into 4 grades: excellent (E), good (G), fair (F), and poor (P). We also analyzed postoperative complications by fracture type. Results: Regarding the postoperative CT images, 189 subjects showed E results, 99 subjects showed G, 18 subjects showed F, and 7 subjects showed P reduction. The rate of operation results graded as E by each fracture type was 66.67% in FI, 52.0% in FII, 64.21% in LI, 62.79% in LII, and 21.74% in C. Complications of FI (7.14%), LII (13.95%), and C (13.04%) groups occurred more than in the FII (4.00%) and LI (4.21%) groups. Conclusion: It seems that the operation result by fracture type was better in the FI, LI, and LII type than the FII and C type; after one month, however, LII type showed more complications than other types. The septal fracture can be thought to affect early reduction results in nasal bone fractures.

• Advances in aircraft and spacecraft science
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• v.7 no.1
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• pp.79-90
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• 2020

The dynamic coupling between shaker and test-article has been investigated by recent research through the so called Virtual Shaker Testing (VST) approach. Basically a VST model includes the mathematical models of the test-item, of the shaker body, of the seismic mass and the facility vibration control algorithm. The subsequent coupled dynamic simulation even if more complex than the classical hard-mounted sine test-prediction, is a closer representation of the reality and is expected to be more accurate. One of the most remarkable benefits of VST is the accurate quantification of the frequency down-shift (with respect to the hard-mounted value), typically affecting the first lateral resonance of heavy test-items, like medium or large size Spacecraft (S/Cs), once mounted on the shaker. In this work, starting from previous successful VST experiences, the parameters having impact on the frequency shift are identified and discussed one by one. A simplified analytical system is thus defined to propose an efficient and effective way of calculating the lower bound frequency shift through a simple equation. Such equation can be useful to correct the S/C lateral natural frequency measured during the test, in order to remove the contribution attributable to the shaker in use. The so-corrected frequency value becomes relevant when verifying the compliance of the S/C w.r.t. the frequency requirement from the Launcher Authority. Moreover, it allows to perform a consistent post-test correlation of the first lateral natural frequency of S/C FE model.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.178-186
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• 2018

The scale effects on the permanent deformations and fractures of structures subjected to impact loadings have been aware by structural engineers for a long time. Experimental investigations have been performed with various structures to demonstrate the effects, but very few are directly related with marine structural elements. Furthermore, the causes of the scale effects have not clearly been answered yet. In this study, to quantify the scale effects on the permanent deflections, lateral collision tests were performed on steel unstiffened plates and the numerical analyses of the tested models were also conducted using a commercial package, Abaqus. After the substantiation of the numerical tool using the test results, a parametric study was carried out considering and neglecting the strain-rate hardening. Based upon the parametric study results, it may be concluded that the main cause of the scale effects on the permanent deflections of steel unstiffened plates subjected to lateral collision loads is the strain-rate effects.