• 대한조선학회논문집
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• 제56권3호
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• pp.231-241
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• 2019

In this study, a simplified analysis method was developed to evaluate the fatigue damage of an ice-going ship under broken ice condition. The global ice load, which is essentially calculated at the design stage of the Arctic vessel, and the hull form information were used to estimate the local ice load acting on the outer-shell of the ship. The local ice load was applied to the finite element analysis model, and the Weibull parameters for the target fatigue point were derived. Finally, fatigue damage was evaluated by applying the S-N curve and the Palmgren-Miner rule. For the verification of the proposed method, numerical analyses using direct approach were performed for the same conditions. A numerical model that implements the interaction between ice and structure was introduced to verify the local ice load and the stress calculated from the proposed method. Finally, the fatigue analyses of the Baltic Sea for actual ice conditions were performed, and the results of the proposed method, the method using numerical analysis, and the LR method were compared.

• Nuclear Engineering and Technology
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• 제46권1호
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• pp.73-80
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• 2014

A concrete cask is an option for spent nuclear fuel interim storage. A concrete cask usually consists of a metallic canister which confines the spent nuclear fuel assemblies and a concrete overpack. When the overpack undergoes a missile impact, which might be caused by a tornado or an aircraft crash, it should sustain an acceptable level of structural integrity so that its radiation shielding capability and the retrievability of the canister are maintained. A missile impact against a concrete overpack produces two damage modes, local damage and global damage. In conventional approaches [1], those two damage modes are decoupled and evaluated separately. The local damage of concrete is usually evaluated by empirical formulas, while the global damage is evaluated by finite element analysis. However, this decoupled approach may lead to a very conservative estimation of both damages. In this research, finite element analysis with material failure models and element erosion is applied to the evaluation of local and global damage of concrete overpacks under high speed missile impacts. Two types of concrete overpacks with different configurations are considered. The numerical simulation results are compared with test results, and it is shown that the finite element analysis predicts both local and global damage qualitatively well, but the quantitative accuracy of the results are highly dependent on the fine-tuning of material and failure parameters.

• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.449-456
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• 2003

In this study, numerical and experimental analysis on the spray atomization characteristics of a GDI injector is performed. For numerical approach, four hybrid models that are composed of primary and secondary breakup model are considered. Concerning the primary breakup, a conical sheet disintegration model and LISA model are used. The secondary breakup models are made based on the DDB model and RT model. The global spray behavior is also visualized by the shadowgraph technique and local Sauter mean diameter and axial mean velocity are measured by using phase Doppler particle analyzer Based on the comparison of numerical and experimental results, it is shown that good agreement is obtained in terms of spray developing process and spray tip penetration at the all hybrid models. However, the hybrid breakup models show different prediction of accuracy in the cases of local SMD and the spatial distribution of breakup.

• Computers and Concrete
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• 제21권6호
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• pp.637-647
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• 2018

Numerical approach using finite element method has been used to evaluate the behaviour of reinforced concrete frame structure subjected to fire. The structure is previously designed in accordance with Eurocode standards for the design of structures for earthquake resistance, for the ductility class M. Thermal and structural response are obtained using a commercially available software ANSYS. Temperature-dependent nonlinear thermal and mechanical properties are adopted according to Eurocode standards, with the application of constitutive model for the triaxial behaviour of concrete with a smeared crack approach. Discrete modelling of concrete and reinforcement has enabled monitoring of the behaviour at a global, as well as at a local level, providing information on the level of damage occurring during fire. Critical regions in frame structures are identified and assessed, based on temperatures, displacements, variations of internal forces magnitudes and achieved plastic deformations of main reinforcement bars. Parametric analyses are conducted for different fire scenarios and different types of concrete aggregate to determine their effect on global deformations of frame structures. According to analyses results, the three-dimensional finite element model can be used to evaluate the insulation and mechanical resistance criteria of reinforced concrete frame structures subjected to nominal fire curves.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.353-360
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• 2002

The objective of this study is to develop a technique that analyzes the global behavior of frame structures with local cracks. The technique is based on frame analysis and uses the stiffness matrix of cracked frame element. An algorithm proposed here analyzes a frame structure with local transverseedge cracks, considering the effects of crack length and location. Stress intensity factors are employed to calculate additional local compliance due to the cracks based on linear elastic fracture mechanics theory, and then this local compliance is utilized to derive the stiffness matrix of the cracked frame element. In order to verify the accuracy and reliability of the proposed approach, numerical results are compared with those of Finite Element Method for the cracked frame element, and the effects of single crack on the behavior of truss structure are also examined.

• 한국해양공학회지
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• 제26권6호
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• pp.74-79
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• 2012

The present study aims at suggesting the systematic approach to analyze the local drag components as the resistance performance characterized by the flow of the ship. In order to identify the local areas, the hull surface is decomposed into SVM (Station-Vertical Section Map) which consists of 20 stations along the longitudinal direction and 20 sections along the vertical direction (from the bottom to the waterline). Successively, on the SVM, the friction and pressure drag coefficients as the components of total drag coefficient have been analyzed for two different hull forms of Wigley and KVLCC by using CFD.

• 한국정보과학회논문지:소프트웨어및응용
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• 제32권3호
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• pp.181-191
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• 2005

본 논문에서는 컴퓨터그래픽으로 구현된 인체에 착용되는 의류의 시뮬레이션을 위한 수치해석알고리즘 및 소프트웨어 개발을 수행하였다. 개발된 알고리즘은 수학적으로 elliptical 흑은 비순차적인 성질을 가지는 두 개의 켤레조화함수(conjugate harmonic functions)들을 사용하여, 지나간 시간단계(time step)에서의 견과에 의존하지 않고 매 순간의 역학적 균형만으로 의류에 형성되는 주름의 형태를 표현한다. Global-local 해석기법을 채택하여 global 스케일에서의 전체적인 변형과 local 스케일에서의 부분적인 변형으로 나누었으며, 이 두 가지 스케일에서의 해석 결과가 선형적으로 중첩될 수 있음을 가정하였다. Global 해석에서는 신체 각 부위의 회전이나 평행이동, 뒤틀림 등의 전반적인 변형에 따른 인체와의 접촉점의 변화와 응력을 고려하였다. Local 해석에서는 국소적인 주름의 형상을 얻기 위해 주름의 진폭등고선과 주름의 방향 사이의 직교성을 가정하여 단순화 시켰다. 본 제안 방법은 불연속적으로 변화하는 두 개의 서로 다른 자세에 대해서도 중간단계 해석을 위한 시간증분의 삽입이 불필요하며, 기존의 방식에서 주로 사용되는 시간적분의 방법을 채택하지 않으므로 연산 시간의 절감과 안정성의 향상이 이루어졌다. 임의의 두 자세 사이의 연속 동작을 시뮬레이션 함에 있어서도 두 정지 자세 사이의 움직임을 보간법으로 구현하여 연속적인 의류의 변형을 구현할 수 있었다.

• Smart Structures and Systems
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• 제15권3호
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• pp.683-698
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• 2015

Railroad bridges form an integral part of railway infrastructure throughout the world. To accommodate increased axel loads, train speeds, and greater volumes of freight traffic, in the presence of changing structural conditions, the load carrying capacity and serviceability of existing bridges must be assessed. One way is through system identification of in-service railroad bridges. To dates, numerous researchers have reported system identification studies with a large portion of their applications being highway bridges. Moreover, most of those models are calibrated at global level, while only a few studies applications have used globally and locally calibrated model. To reach the global and local calibration, both ambient vibration tests and controlled tests need to be performed. Thus, an approach for system identification of a railroad bridge that can be used to assess the bridge in global and local sense is needed. This study presents system identification of a railroad bridge using free vibration data. Wireless smart sensors are employed and provided a portable way to collect data that is then used to determine bridge frequencies and mode shapes. Subsequently, a calibrated finite element model of the bridge provides global and local information of the bridge. The ability of the model to simulate local responses is validated by comparing predicted and measured strain in one of the diagonal members of the truss. This research demonstrates the potential of using measured field data to perform model calibration in a simple and practical manner that will lead to better understanding the state of railroad bridges.

• 한국생산제조학회지
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• 제21권1호
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• pp.26-32
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• 2012

In the present study, the stencil printing process using solder paste are numerically analyzed. The key design parameters in the stencil printing process are the printing conditions, stencil design, and solder paste properties. Among these parameters, the effects of printing conditions including the squeegee angle and squeegee pressure are investigated through finite element (FE) analysis. However, the FE analysis for the stencil printing process requires tremendous computational loads and time because this process carries micro-filling through thousands of micro-apertures in stencil. To overcome this difficulty in simulation, the present study proposes a two-step approach to sequentially perform the global domain analysis and the local domain analysis. That is, the pressure development under the squeegee are firstly calculated in the full analysis domain through the global analysis. The filling stage of the solder paste into a micro-aperture is then analyzed in the local analysis domain based on the results of the preceding global analysis.

• Structural Engineering and Mechanics
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• 제65권3호
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• pp.327-334
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• 2018

In the steel structures design, beam-to-column connections are usually considered either rigid or pinned, while their actual behavior lies between these two ideal cases. This consideration has a major influence on the results of the local and the global behavior of steel structures. This influence is noticed in the case of a static analysis, and has an important effect in the case of a dynamic analysis. In fact, pinned and rigid nodes can be considered as two specific cases of a semi-rigid behavior. To study the efficiency of the classification adopted in Eurocode 3, a numerical simulation of semi-rigid nodes has been carried out using the software ANSYS. In the aim to validate this simulation, the numerical results are compared to those of an analytical approach. After that, the validated numerical simulation has been used, to evaluate the efficiency of the classification adopted by the Eurocode 3, regarding semi-rigid connections. Finally, a new method is proposed to define a more accurate evaluation about semi-rigid connections.