• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.31 no.2 s.257
• /
• pp.277-284
• /
• 2007

The steam generator in a nuclear power plant is a large heat exchanger that uses heat from a reactor to generate steam to drive the turbine generator. Rupture of a steam generator tube can result in release of fission products to environment outside. Therefore, an accurate integrity assessment of the steam generator tubes with cracks is of great importance for maintaining the safety of a nuclear power plant. The steam generator tubes are supported at regular intervals by support plates and rotations of the tubes are restrained. Although it has been reported that the limit load for a circumferential crack is significantly affected by boundary condition of the tube, existing limit load solutions do not consider the restraining effect of support plate correctly. In addition, there are no limit load solutions for circumferential cracks in U-bend region with the effect of the support plate. This paper provides detailed limit load solutions for circumferential cracks in top of tube sheet and the U-bend regions of the steam generator tube with the actual boundary conditions to simulate the restraining effect of the support plate. Such solutions are developed based on three dimensional finite element analyses. The resulting limit load solutions are given in a polynomial form, and thus can be simply used in practical integrity assessment of the steam generator tubes.

• Journal of the Society of Naval Architects of Korea
• /
• v.55 no.4
• /
• pp.289-296
• /
• 2018

The offshore subsea platforms are connected to subsea pipelines to transport gas/oil from wells. The pipe is a multilayered structure of polymer and steel for compensating both flexibility and strength. The pipe also requires reinforcement structures to endure the extreme environmental conditions. A vertebrae structure of bend restrictors is one of the reinforcement structures installed to protect the subsea pipe from excessive bending deformations. In this study, structural behaviors of the subsea pipeline with bend restrictors are investigated by the multi-body contact analysis in Abaqus 6.14-2. Contact forces of each bend restrictor extracted from the multi-body contact analysis can be boundary conditions for topology design optimization in Altair Hyperworks 13.0 Hypermesh-Optistruct. Multiple design constraints are considered to obtain a manufacturable design with efficient material usage. Through the multi-body contact analysis with optimized bend restrictors, it is confirmed that the bending performance of the optimized design is enhanced.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.36 no.1
• /
• pp.41-47
• /
• 2020

Purpose: The purpose of this study was to evaluate the flexural strength and reliability of highly translucent colored zirconia for all ceramic restoration. Materials and Methods: Bar-shaped specimens (25 × 4 × 2.5 mm) were prepared from highly translucent monolithic zirconia. Three experimental groups were set up according to color (shade A0, A1, and A3). For each group, 20 specimens were prepared. Flexural strength was determined using a 3-point flexural test and results were analyzed with one-way ANOVA test. Weibull statistical analysis provided 2 parameter estimates: Weibull modulus and characteristic strength. X-ray diffraction (XRD) analysis was performed. Results: There was statistically significant difference between uncolored (Shade A0) and colored (shade A1 and A3) (P < 0.05), but there was no difference between colored groups (P > 0.05). The uncolored group had higher reliability compared with colored study groups. On x-ray diffraction analysis of each group, typical peaks of tetragonal phase appeared in all groups. Conclusion: Within the limitations of this in vitro study, coloring highly translucent zirconia had significant effect on flexural strength and reliability. Therefore, clinicians should be careful when using highly translucent colored zirconia to prevent breakage of veneering ceramic and enhance aesthetics.

• Journal of the Society of Naval Architects of Korea
• /
• v.32 no.4
• /
• pp.64-72
• /
• 1995

Sizing design sensitivity analysis of structures subjected to the harmonic vibration is performed using adjoint variable method. Constraint is the stress and sizing design variables are thickness, bending moment of inertia, and cross-sectional area of structures. Accurate sensitivities are computed and plotted sensitivity can be used as a design guidance tool. The accuracy of sensitivities is verified by the finite difference values. Also, optimal design of three-bar structure is performed using the computed sensitivity and feasible direction method while satisfying constraints and obtaining the minimum weight.

• Journal of the Society of Naval Architects of Korea
• /
• v.29 no.2
• /
• pp.115-122
• /
• 1992

A sandwich element is a special Hybrid structural form of the composite construction, which is consisted of three main parts : thin, stiff and relatively high density faces separated by a thick, light, and weaker core material. In a sandwich construction, the shear deformation of the faces. Therefore, in the calculation of the bending stiffness, the shear effect should be included. In this paper, the minimum weight is selected as an object function, as the weight critical structures are usually composed of these kind of construction. To obtain the minimum weight of sandwich panel, the principle of minimum potential energy is used and as for the design constraints, the allowable bending stress of face material, the allowable shear stress of core material, the allowable value of panel deflection and the wrinkling stress of faces are adopted, as well as the different boundary conditions. For the engineering purpose of sandwich panel design, the results are tabulated, which are calculated by using the nonlinear optimization technique SUMT.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.35 no.1
• /
• pp.39-45
• /
• 2015

Applications of smart sensors have been extended to safety systems in the aerospace, transportation and civil engineering fields. In particular, structural health monitoring techniques using smart sensors have gradually become necessary and have been developed to prevent dangers to human life and damage to assets. Generally, smart sensors are based on electro-magnets and have several weaknesses, including electro-magnetic interference and distortion. Therefore, fiber optic sensors are an outstanding alternative to overcome the weaknesses of electro-magnetic sensors. However, they require expensive devices and complex systems. This paper proposes a new, affordable and simple sensor system that uses a single fiber to monitor pressures at multiple-points. Moreover, a prototype of the sensor system was manufactured and tested for a feasibility study. Based on the results of this experimental test, a relationship was carefully observed between the bend loss conditions and light-intensity. As a result, it was shown that impacts at multiple-points could be monitored.

• Composites Research
• /
• v.26 no.2
• /
• pp.85-90
• /
• 2013

This paper presents the fabrication and 3-point flexion testing of carbon fiber reinforced polymer (CFRP) composite face/aluminum honeycomb core sandwich panels. Specimen sandwich panels were fabricated with three honeycomb types (3.18 mm, 4.76 mm, and 6.35 mm cell size) and three panel radii (flat, r = 1.6 m, r = 1.3 m). The curved sandwiches were fabricated normally with the core in the W-direction. The tensile mechanical properties of the CFRP $2{\times}2$ twill fabric face laminate were evaluated (modulus, strength, Poisson's ratio). The measured values are comparable to other CFRP fabric laminates. The flat sandwich 3-point flexion test core shear strength results were 11-30% lower than the manufacturer published data; the test set-up used may be the cause. With a limited sample size, the 1.3 meter panel curvature appeared to cause a 0.8-3.8% reduction in ultimate core shear strength compared to a flat panel.

• The Journal of the Korea Contents Association
• /
• v.11 no.12
• /
• pp.326-334
• /
• 2011

The aim of the study was to investigate the thickness of deep neck muscles during neck endurance tests using ultrasonography images to assess muscle sizes in persons with or without neck pain experience. Sixty-five university students volunteered for the study. The thicknesses of longus colli, longus capitis, semispinalis and cervical multifidus were assessed bilaterally using diagnostic ultrasound equipment during each endurance test. Participants were divided into two groups based on their Neck Pain(NP) experience; 45 subjects of those had no experience of NP (Group1) whereas 20 subjects of those reported NP experience sometime in their lives (Group2). Endurance time of both neck flexion and extension tests in Group1 showed significantly longer than Group's (p<0.01). The thicknesses of deep neck flexors and extensors were observed smallest at the terminal of endurance tests in general. Only left longus colli was found to be significantly smaller at rest in subjects of Group2 than Group 1's (P=0.02). The size difference between at contraction and the terminal of right longus capitis was observed bigger in subjects of group1 than subjects in group2. Future studies are needed to conduct with clinical subjects to assess contraction patterns of neck muscles.

• Journal of Digital Convergence
• /
• v.17 no.3
• /
• pp.463-471
• /
• 2019

The purpose of this study was to investigate the effect of muscle imbalance on motion of back squat. The isokinetic muscle strength of the 8 subjects was recorded for the knee flexion/extension by the cybex 770 dynamometer. Each subject performed 3 back squats with the long barbell with an intensity of 25% body weight(BW), 50%BW, 100%BW, 125%BW. During the back squat through the recorded kinematic data the subjects' maximum flexion and extension knee angle, center of mass displacement and V-COP were calculated for evaluation of the stability of the movement. For the statistical analysis independent t-test was used. Knee flexion angle and COM displacement are dominated by the reciprocal muscle ratio. V-COP factor was dominated by bilateral extension deficit. Based on the results we can know that as the intensity of the squat increased to a level control was difficult because the muscles' imbalance influenced the movement.

• Journal of the korean Society of Automotive Engineers
• /
• v.18 no.4
• /
• pp.1-17
• /
• 1996

자동차의 안전에 대한 연구는 객실의 변형제한과 승객의 감속도 축소를 위한 여러가지 구조부재의 에너지 흡수능력 및 흡수 메카니즘을 연구하는데 초점이 맞추어져 왔다. 그 이유는 충돌사고시에 인명을 보호하기 위해서는 차제변형에 의한 물리적 접촉의 회피 뿐 아니라 충돌에너지를 적절히 흡수조절하여 충돌력을 감소시키도록 구조부재를 설계함으로써 충돌안전성이 확보되기 때문이다. 충돌에너지 흡수 특성은 구조부재의 단면 형상과 재질에 따라 달라지며 압괴모드도 구분되어진다. 즉, 복합재료의 압축붕괴특성은 금속이나 플라스틱 재질과는 다르다. 일반적으로 복합재는 재질의 파손으로 에너지가 흡수되지만 금속재는 소성변형으로 에너지를 흡수한다. 이때의 붕괴양상은 작용하중에 따라 축방향 붕괴, 굽힘붕괴, 측면붕괴의 경우는 정규압괴모드(compact mode) 및 불규칙압괴모드(noncompact mode)로 나뉘고, 원통쉘의 경우는 축대칭모드 및 다이아몬드형 모드 등으로 나뉠수 있다. 원형 및 사각 튜브는 광범위한 형상비와 후폭비를 가지도록 제작할 수 있으며 산업전반에 걸쳐 널리 쓰이므로 충돌특성 연구의 대상으로 많은 연구들이 진행되어 왔다. 또한, 충돌특성의 해석을 위한 이론적 모델이 제시되었으며 계속적인 보완이 이루어져 오고 있다.