• Structural Engineering and Mechanics
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• 제46권1호
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• pp.53-73
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• 2013

Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.912-917
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• 2003

In this paper a new truss modeling technique for describing the beam shear resistance mechanism is proposed based on the reinterpretation of the well-known relationship between shear and the rate of change of bending moment in a reinforced concrete beam subjected to combined shear and moment loads. The core of the model is that a new perspective on the shear resistance can be gained by viewing the internal stress filed in terms of the superposition of two base components of shear resistance; arch action and beam action. The arch action can be described as a simple tied-arch which is consisted of a curved compression chord and a tension tie of the longitudinal steel, while the beam action between the two chords can be modeled as a membrane shearing element with forming a smeared truss action. The compatibility of deformation associated to the two action is taken into account by employing an experimental factor or internal state force factor a. Then the base equation of V=dM/dx is numerically duplicated. The new model was examined by the 362 experimental results. The shear strength predicted by the internal force state factor a show better correlation with the tested values than the present shear design.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1243-1248
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• 2011

내부결함은 주조제품의 강도 및 피로 수명에 있어 상당한 영향을 미치기 때문에 주조공정에서 주요 관심사 이다. 일반적으로 내부결함은 응력집중을 발생시키며 균열의 시작점이 되므로 피로 수명과 같은 기계적 거동에 있어 수축공과 같은 결함을 이해하는 것이 중요하다. 본 논문에서는 내부결함을 고려한 인장시편에 대해 피로시험을 수행하고 주조결함을 고려할 때의 특정하중피로노치 계수를 산정하였다. 실제 내부결함은 산업용 CT 장비를 통해서 확인하였으며 확인된 결함은 형상단순화법에 의해 타원체로 단순화 하고 응력해석과 피로해석을 수행하였다. 그 결과 우리가 제안한 방법이 기계적 거동에 있어 내부결함의 영향을 조사하고 피로수명 등을 예측함에 있어 유용함을 확인할 수 있었다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.9-13
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• 2003

The objective of this study is structural analysis of rope brake for elevator. The finite element model was developed to compute the stress, strain and friction force for rope brake. The ANSYS code was used for this analysis. In order to structural analysis of rope brake, many variables such as internal pressure, boundary condition, load condition and constraints were considered.

• 한국공작기계학회논문집
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• 제14권1호
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• pp.89-94
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• 2005

The objective of this study is structural analysis of rope brake by spring type. The finite element model was developed to compute the stress, strain and friction force for rope brake by spring type. The ANSYS code was used for this analysis. In order to structural analysis of rope brake, many variables such as internal pressure, boundary condition load condition and constraints were considered.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.150-155
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• 2004

The objective of this study is structural analysis of rope brake by spring type. The finite element model was developed to compute the stress, strain and friction force for rope brake by spring type. The ANSYS code was used for this analysis. In order to structural analysis of rope brake, many variables such as internal pressure, boundary condition, load condition and constraints were considered.

• 대한한방내과학회지
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• 제41권6호
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• pp.993-1014
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• 2020

Objective: Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. Antioxidant stress and inflammatory reactions are important causes of neurodegenerative diseases and are major causes of PD. Many animal experiments have been aimed at treating PD using the antioxidant effects of various traditional medicines and dietary supplements. This review reports the research investigating the antioxidant effects of herbs in in vivo PD models. Methods: The study consisted of a database search for articles related to PD and herbal treatments using the OASIS, NDSL, KTKP, Korean KISS, PubMed, Science Direct, CNKI, Wanfang, and J-STAGE databases. The search period was limited from the start of the search engine application to November 14, 2019. Studies were selected to confirm the antioxidant effects of herbal medicines in an in vivo PD model. Results: Eighty-two studies were summarized for plant species, extracts (or compounds), animal models, neurotoxins, and functional results. The most frequently used herbal materials were Bacopa monnieri, Camellia sinensis, Centella asiatica, and Withania somnifera. MPTP and 6-OHDA were the most commonly used neurotoxins for inducing PD. Most studies confirmed an increased expression and activation of antioxidant enzymes and a decrease in oxidative stress. Herbal materials showed their antioxidant effects regardless of the order of treatment and confirmed their possible use as treatments for the prevention and treatment of neurodegeneration. Conclusion: Many herbal medicines have antioxidant effects and are likely to be effective in delaying neurodegenerative damage by inhibiting or reducing oxidative stress by expression of antioxidant enzymes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.604-609
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• 2003

Turbulent temperature field in a channel with wall injection has been investigated using dynamic mixed model(DMM). This flow is pertinent to internal flows inside the hybrid rocket motors. In general, the results obtained with DMM are in better agreement with DNS results compared to those of dynamic Smagorinsky model(DSM). Such favorable features of DMM are attributed to the fact that it explicitly calculates the modified Leonard stress term which takes care of the local interaction between resolved and SGS stresses and only models the remaining cross and SGS Reynolds stress terms.

• 대한기계학회논문집A
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• 제30권9호
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• pp.1134-1141
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• 2006

This paper presents the model for evaluating restraint effect of pressure induced bending (PIB) on the circumferential through-wall crack opening displacement (COD), which considers plastic behavior of crack. This study performed three-dimensional elastic-plastic finite element (FE) analyses for different crack angle, restraint length, pipe geometry, stress level, and material conditions, and evaluated the influence of each parameter on the PIB restraint effect on COD. Based on these evaluations and additional perfectly-plastic FE analyses, a closed-form model to evaluate the restraint effect of PIB on the plastic crack opening of circumferential through-wall crack, was proposed as functions of crack angle, restraint length, radius to thickness ratio, axial stress corresponding to an internal pressure, and normalized COD evaluated from linear-elastic crack opening condition.

• Journal of Mechanical Science and Technology
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• 제20권3호
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• pp.319-328
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• 2006

A simple approximation method for the stress intensity factor at the tip of the axial semielliptical cracks on the cylindrical vessel is developed. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. For these, 3-D finite-element analyses are performed to obtain the stress intensity factors for various surface cracks with t/R=0.1. The approximation solutions are within $\pm2.5%$ of the those of finite element analysis using symmetric model of one-forth of a vessel under pressure loading, and 1-3% higher under pressurized thermal shock condition. The analysis results confirm that the approximation method provides sufficiently accurate stress intensity factor values for the axial semi-elliptical flaws on the surface of the reactor pressure vessel.