• Journal of Korean Association for Spatial Structures
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• v.7 no.6
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• pp.69-74
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• 2007

Recently, to improve performance and strength of circular steel columns, application of concrete-filled steel tube(CFT) type are gradually increased. To accurately predict the plastic design of concrete-filled steel tube columns, a plasticity model is required which can be describe large deformation behavior of concretes and steels. In this study, elastic-plastic large deformation analysis is developed by using the plasticity model of structural steels, and accurate and validity of the developed program is verified by comparing between the experiment and the analysis for concrete-filled steel tube column. In concrete-filled steel tube columns, influence of initial deflection on ultimate strength behavior is investigated by using developed program.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1366-1371
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• 2008

Four simulation models of plastic plate heat exchangers are designed and simulated. The flat plate type heat exchanger is designed as the reference model in order to evaluate how much thermal performance increases. The turbulence promoter type heat exchanger is fabricated with cylindrical-type vortex generators and rib-type turbulence promoters. The corrugate type is obtained from the conventional stainless steel compact heat exchangers, which are called the herringbone-type compact heat exchangers. The dimple type heat exchanger has a number of dimples on its surface. In this study, the flow and heat transfer characteristics of the plastic plate heat exchanger are investigated using numerical simulation and compared with experimental results. The flows are assumed as a three-dimensional, incompressible and turbulent model. The standard k-$\varepsilon$ model is used as the turbulent flow modeling, the SIMPLE algorithm is used to treat the coupling between pressure and velocity, and first order upwind scheme is used for discretization of momentum, turbulent and energy. The computational analysis and experimental results both show that the friction coefficient and Nu number is highest in the corrugate type.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.11
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• pp.1813-1821
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• 2004

Until now, the 40% of wall thickness criterion, which is generally used for the plugging of steam generator tubes, has been applied only to a single cracked geometry. In the previous study by the authors, a total number of 9 local failure prediction models were introduced to estimate the coalescence load of two collinear through-wall cracks and, then, the reaction force model and plastic zone contact model were selected as the optimum ones. The objective of this study is to estimate the coalescence load of two collinear through-wall cracks in steam generator tube by using the optimum local failure prediction models. In order to investigate the applicability of the optimum local failure prediction models, a series of plastic collapse tests and corresponding finite element analyses for two collinear through-wall cracks in steam generator tube were carried out. Thereby, the applicability of the optimum local failure prediction models was verified and, finally, a coalescence evaluation diagram which can be used to determine whether the adjacent cracks detected by NDE coalesce or not has been developed.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.617-624
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• 2008

Well-designed steel moment connections will undergo local buckling before they exhaust their available rotation capacity, and inelastic post-buckling deformation plays a major role in defining the connection rotation capacity. An approximate analytical method to model strength degradation and failure of beam plastic hinges due to local buckling and estimation of the seismic rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames under both monotonic and cyclic loading conditions is proposed in this study. This method is based on the plastic mechanism and a yield line plastic hinge (YLPH) model whose geometry is determined using the shapes of the buckled plastic hinges observed in experiments. The proposed YLPH model was developed for the improved WUF-W and RBS connections and validated in comparison with experimental data. The effects of the beam section geometric parameters on the rotation capacity were discussed in the companion paper (parametric studies).

• Archives of Craniofacial Surgery
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• v.13 no.2
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• pp.125-129
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• 2012

Purpose: Methylmethacrylate is the most commonly used alloplastic material in cranioplasty. However during the polymerization of methylmethacrylate, a significant exothermic reaction takes place. This reaction may result in thermal injury to the brain tissue and other soft tissues. Also it is difficult to make three-dimensional methylmethacrylate implant that is perfectly matched to the defect during the operation time. We report on the molding technique of methylmethacrylate implant using plaster mold and the rapid prototyping model in cranioplasty. Methods: A 44-year-old male was referred to the department for severe frontal hollowness. He was involved in an automobile accident resulting in large frontal bone defect with irregular margin. The preformed patient-specific methylmethacrylate implant was made using plaster mold and the rapid prototyping model before the operative day. The methylmethacrylate implant was placed in the frontal defect and rigidly fixed with miniplates and screws on the operative day. Results: The operation was performed in an hour. In the 6 months follow-up period, there were no complications. Patient was satisfied with the results of cranioplasty. Conclusion: Safe cranioplasty was performed with the preformed patient-specific methylmethacrylate implant using plaster mold and the rapid prototyping model. The result of this method was satisfactory, aesthetically and functionally.

• Archives of Plastic Surgery
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• v.34 no.6
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• pp.777-784
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• 2007

Purpose: For a minor degree of mandibular prognathism, mandibular anterior segmental osteotomy (ASO), usually extracting the bilateral premolars, has been performed frequently to correct malocclusion of the anterior teeth. Preoperative planning using cephalometry and a dental model is very important for such a orthognathic surgery. Depending on the specific preoperative mock surgery with the dental model, ASO, with ipsilateral unitooth extraction, is defined to be feasible and performed for ten patients. The comparisons of its preoperative and postoperative analysis of clinical photographs, dental casts, and lateral cephalograms, for soft tissue profiles, skeletal and dental relationships are described in the following, and its clinical applications are noted. Methods: From March 1, 2004, to March 31, 2006, We performed 10 mandibular ASO by extraction of ipsilateral unitooth to improve their lower facial profiles and the lip relationships. Patient age ranged from 19 to 33 years, with a mean age of 25.6 years. Two were males and eight were females. Results: All patients were satisfied with aesthetic and occlusal changes postoperatively. Significant and persistent decrease in the SNB and interincisal angle were observed in the postoperative cephalometries. The soft tissue profiles also were improved and near Ricketts's esthetic line. Other combined procedures include nine genioplasties, two rhinoplasties, and one blepharoplasty. One patient complained of transient unilateral inferior mental nerve paresthesia. There were no other significant complications or relapses throughout the follow-up period(6-20 months). Conclusion: Mandibular ASO, extracting the ipsilateral unitooth, was performed for ten patients to correct mild mandibular prognathism. The amount of setback of the mandibular anterior portion was 2 to 3 mm, and satisfactory results were obtained combined with genioplasties.

• Archives of Plastic Surgery
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• v.46 no.3
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• pp.228-234
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• 2019

Background The management of flexor tendon injuries has evolved in recent years through industrial improvements in suture materials, refinements of repair methods, and early rehabilitation protocols. However, there is no consensus on the ideal suture material and technique. This study was conducted to compare the tensile strength, repair time, and characteristics of 4-strand cruciate, modified Kessler, and 4-strand horizontal intrafiber barbed sutures for flexor tenorrhaphy with a 12-mm suture purchase length in an animal model. Methods The right third deep flexors of 60 adult Leghorn chicken feet were isolated and repaired with a 12-mm suture purchase length. The tendons were randomly assigned to three groups of equal number (n=20 each). Groups 1 and 2 received 4-strand cruciate and modified Kessler repair with conventional suture materials, respectively. A 4-strand horizontal intrafiber barbed suture technique was used in group 3. The repaired tendons were biomechanically tested for tensile strength, 2-mm gap resistance, and mode of failure. Repair times were also recorded. Results The maximum tensile strength until failure was $44.6{\pm}4.3N$ in group 1, $35.7{\pm}5.2N$ in group 2, and $56.7{\pm}17.3N$ in group 3. The barbed sutures were superior to the other sutures in terms of the load needed for 2-mm gap formation (P<0.05). Furthermore, the barbed sutures showed the shortest repair time (P<0.05). Conclusions This study found that 4-strand horizontal intrafiber barbed suture repair with a 12-mm purchase length in a chicken flexor tendon injury model showed promising biomechanical properties and took less time to perform than other options.

• KCI Concrete Journal
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• v.13 no.2
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• pp.67-74
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• 2001

In this study, a numerical model for the simulation of reinforced concrete columns subject to cyclic loading is presented. The model consists of three separate models representing concrete, reinforcing steel bars and bond-slip between a reinforcing bar and ambient concrete. The concrete model is represented by the plane stress plastic-damage model and quadrilateral finite elements. The nonlinear steel bar model embedded in truss elements is used for longitudinal and transverse reinforcing bars. Bond-slip mechanism between a reinforcing bar and ambient concrete is discretized using connection elements in which the hysteretic bond-slip link model defines the bond stress and slip displacement relation. The three models are connected in finite element mesh to represent a reinforced concrete structure. From the numerical simulation, it is shown that the proposed model effectively and realistically represents the overall cyclic behavior of a reinforced concrete column. The present plastic-damage concrete model is observed to work appropriately with the steel bar and bond-slip link models in representing the complicated localization behavior.

• Structural Engineering and Mechanics
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• v.11 no.4
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• pp.393-406
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• 2001

The present paper discusses the behavior of the reinforced concrete beams subjected to torsion by applying the endochronic plastic model in conjunction with the softened truss model. The endochronic constitutive equations are developed to describe the behavior of concrete. The mechanical behavior of concrete is decomposed into hydrostatic part and deviatoric part. New definition of the bulk modulus and the shear modulus are defined in terms of compressive strength of concrete. Also, new deviatoric hardening function is developed. Then, the endochronic constitutive equations of concrete are applied with the softened truss model for the behavior of the reinforced concrete beams subjected to torsion. The theoretical results obtained based on the present model are compared with the experimental data. The present model has shown the ability to describe the behavior of reinforced concrete beams subjected to torsion.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.4
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• pp.129-134
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• 2001

It is essential to predict the welding deformation at assembly stage, to increase productivity through mechanization and automation effectively. A practical analysis method appled for production engineering was proposed to simulate the deformation of arc welding, with an analytical model using finite element method solving thermal-elastic-plastic behavior. In this research, for accurate assembling, 3-D thermal-elastic-plastic finite element model is used to simulate the out-of-plane deformation caused by arc welding. Efforts have been made to find out the efficient method to improve the reliability and accuracy of the numerical calculation. Each of theories of small and large deformation is applied in solving 3-D thermal-elastic-plastic problem to compare with their efficiency about calculation imes and solution accuracy. When solid elements are used in a bending problem of a plate, phenomenon that the predictive deformation is more than that of actual survey is observed. To prevent this phenomenon, reduced integration method for element is employed instead of full integration that is generally used in 3-D thermal-elastic-plastic analysis.