• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.824-830
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• 2003

The Power Flow Finite Element Method(PFFEM) offers very promising results in predicting the vibration responses of system structures, and the first PFFEM software, PFADS has been developed in Seoul National University for the vibration predictions and analysis of coupled system structures in medium-to-high frequency ranges. PFFEM is numerical method which solves energy governing equation using finite element technique for complicated structures where the exact solutions are not available. Through the upgrades, the current version PFADS R3 could cover the general beam and plate structures including various kinds of beam-plate rigid joints, spring-damper connection and rigid body connection within beam and plate in addition. This software is composed of three parts; translator, model converter and solver. The translator makes its own FE-model from bulk data of commercial FE software, and the model converter is used to convert FE-model to PFFE-model automatically. The solver calculates vibrational energy density and intensity for PFFE-model by solving global matrix equations of PFFEM. For the applications of PFADS R3, two vehicle models and a container model are examined with respect to major parameters, and reliable results are obtained.

• Journal of Welding and Joining
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• 제26권6호
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• pp.74-80
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• 2008

A finite element modeling approach has been described for the simulation and analysis of the micron-scaled solid particle impact behavior in kinetic spraying process, using an explicit code (ABAQUS 6.7-2). High-strain-rate plastic deformation and interface bonding features of the copper, nickel, aluminum, and titanium were investigated via FEM in conjunction with the Johnson-Cook plasticity model. Different aspects of adiabatic shear instabilities of the materials were characterized as a concept of thermal boost-up zone (TBZ), and also discussed based upon energy balance concept with respect to relative recovery energy (RRE) for the purpose of optimizing the bonding process.

• Nuclear Engineering and Technology
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• 제47권5호
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• pp.559-566
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• 2015

The thermalehydraulic characteristics for the CANadian Deuterium Uranium Flexible (CANFLEX)-burnable poison (BP) fuel channel, which is loaded with a BP at the center ring based on the CANFLEX-RU (recycled uranium) fuel channel, are evaluated and compared with that of standard 37-element and CANFLEX-NU (natural uranium) fuel channels. The distributions of fuel temperature and critical channel power for the CANFLEX-BP fuel channel are calculated using the NUclear Heat Transport CIRcuit Thermohydraulics Analysis Code (NUCIRC) code for various creep rate and burnup. CANFLEX-BP fuel channel has been revealed to have a lower fuel temperature compared with that of a standard 37-element fuel channel, especially for high power channels. The critical channel power of CANFLEX-BP fuel channel has increased by about 10%, relative to that of a standard 37-element fuel channel for 380 channels in a core, and has higher value relative to that of the CANFLEX-NU fuel channel except the channels in the outer core. This study has shown that the use of a BP is feasible to enhance the thermal performance by the axial heat flux distribution, as well as the improvement of the reactor physical safety characteristics, and thus the reactor safety can be improved by the use of BP in a CANDU reactor.

• 한국농공학회지
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• 제41권4호
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• pp.104-112
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• 1999

Tensile behavior in concrete has been neglected until recently. However, the effect of tensile stresses in concrete must be considered where the member primarily carries tensile forces or when ultimate strength is affected by the cracking history. In this paper, a series of experiments were performed with a reinforced rectangular beams of 15 specimens in order to investigate the effect of tension stiffening into the nonlinear analysis and cracking behavior. The experimental results were analyzed in terms of load-deflection curves and strain fracture energy with respect to the main experimental variables such as types of specimen, strength of concrete and steel ration. The results from experiments and finite element analysis were compared in terms of load-deflection relationship and cracking pattern. The results are as follows ; The tension stffening effects of reinforced concrete beams were observedc up to yielding of members after cracking showing strain energy difference of 35 % at the beam of 0.57% steel ratio compared with that of beam ignoring the tension stiffening effect. The tension stiffening of concrete strength 400kgf/$\textrm{cm}^2$ and 600kgf/$\textrm{cm}^2$ increased by 8% and 13%, respectively, compared with that of concrete strength 200kgf/$\textrm{cm}^2$. The tension stiffening effects were greater at a ductile member rather than a brittle one. The load-deflection results of finite element analysis showed very similar results from experiment. The crack growth and pattern might be predicted from the nonlinear finite element analysis considering concrete stiffening.

• 콘크리트학회논문집
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• 제17권6호
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• pp.1053-1064
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• 2005

The mechanical damage of concrete is normally attributed to the formation of microcracks and their propagation and coalescence into macroscopic cracks. This physical degradation is caused from progressive and hierarchical damage of the microstructure due to debonding and slip along bimaterial interfaces at the mesoscale. Their growth and coalescence leads to initiation of hairline discrete cracks at the mesoscale. Eventually, single or multiple major discrete cracks develop at the macroscale. In this paper, from this conceptual model of mechanical damage in concrete, the computational efforts were made in order to characterize physical cracks and how to quantify the damage of concrete materials within the laws of thermodynamics with the aid of interface element in traditional finite element methodology. One dimensional effective traction/jump constitutive interface law is introduced in order to accommodate the normal opening and tangential slips on the interfaces between different materials(adhesion) or similar materials(cohesion) in two and three dimensional problems. Mode I failure and mixed mode failure of various geometries and boundary conditions are discussed in the sense of crack propagation and their spent of fracture energy under monotonic displacement control.

• Earthquakes and Structures
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• 제8권3호
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• pp.699-712
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• 2015

Bracing structures with off-centre bracing system is one of the new resistant systems that frequently used in the frame with pin connections. High ductility, high-energy dissipation and decrease of base shear are advantages of this bracing system. However, beside these advantages, reconstruction and hard repair of off-centre bracing system cause inappropriate performance in the earthquake. Therefore, in this paper, the goal is investigating the behavior of this type of bracing system with ductile element (circular dissipater), in order to providing replacement of damaged member without needing repair or reconstruction of the general system. To achieve this purpose, some numerical studies have been performed using ANSYS software, a frame with off-centre bracing system and optimum eccentricity (OBS-C-O) and another frame with the same identifications without ductile element (OBS) has been created. In order to investigate precisely on the optimum placement of circular elements under monotonic load again three steal frames were modeled. Furthermore, the behavior of this general system investigated for the first time, linear and nonlinear behavior of these two steel frames compared to each other, to achieve the benefit of using the circular element in an off-centre bracing system. Eventually, the analytical results revealed that the performance of steel ring at the end of off-centre braces system illustrating as a first defensive line and buckling fuse in the off-centre bracing system.

• Nuclear Engineering and Technology
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• 제48권1호
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• pp.43-54
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• 2016

In the present paper, development of the three-dimensional (3D) computational code based on Galerkin finite element method (GFEM) for solving the multigroup forward/adjoint diffusion equation in both rectangular and hexagonal geometries is reported. Linear approximation of shape functions in the GFEM with unstructured tetrahedron elements is used in the calculation. Both criticality and fixed source calculations may be performed using the developed GFEM-3D computational code. An acceptable level of accuracy at a low computational cost is the main advantage of applying the unstructured tetrahedron elements. The unstructured tetrahedron elements generated with Gambit software are used in the GFEM-3D computational code through a developed interface. The forward/adjoint multiplication factor, forward/adjoint flux distribution, and power distribution in the reactor core are calculated using the power iteration method. Criticality calculations are benchmarked against the valid solution of the neutron diffusion equation for International Atomic Energy Agency (IAEA)-3D and Water-Water Energetic Reactor (VVER)-1000 reactor cores. In addition, validation of the calculations against the $P_1$ approximation of the transport theory is investigated in relation to the liquid metal fast breeder reactor benchmark problem. The neutron fixed source calculations are benchmarked through a comparison with the results obtained from similar computational codes. Finally, an analysis of the sensitivity of calculations to the number of elements is performed.

• 설비공학논문집
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• 제18권3호
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• pp.211-217
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• 2006

The three-dimensional numerical analysis has been carried out to figure out the effect of the thermoelectric element thickness on the thermal performance of the thermo-electric micro-cooler. The small-size and column-type thermoelectric cooler is considered. It is known that tellurium compounds currently have the highest cooling performance around the room temperature. Thus, in the present study, $Bi_{2}Te_{3}$ and $Sb_{2}Te_{3}$ are selected as the n- and p-type thermoelectric materials, respectively. The thermoelectric leg considered is less than $20{\mu}m$ thick. The thickness of the leg may affect the thermal and electrical transport through the interfaces between the leg and metal conductors. The effect of the thermoelectric element thickness on the thermal performance of the cooler has been investigated with parameters such as the temperature difference, the current, and the cooling power.

• 전기학회논문지
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• 제58권10호
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• pp.2011-2015
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• 2009

In an insulating dielectric liquid such as transformer oil, space charge injection and propagation were analyzed under the Fowler-Nordheim and Richardson-Dushman's thermal emission charge injection conditions for blade-plane electrodes stressed by a step voltage. The governing equations were composed of all five equations such as the Poisson's equation for electric fields, three continuity equations for electrons, negative, and positive ions, and energy balanced equation for temperature distributions. The governing equations for each carrier, the continuity equations, belong to the hyperbolic-type PDE of which the solution has a step change at the space charge front resulting in numerical instabilities. To decrease these instabilities, the governing equations were solved simultaneously by the Finite Element Method (FEM) employing the artificial diffusion scheme as a stabilization technique. Additionally, the terminal current was calculated by using the generalized energy method which is based on the Poynting's theorem, and represents more reliable and stable approach for evaluating discharge current. To verify the proposed method, the discharge phenomena were successfully applied to the blade~plane electrodes, where the radius of blade cap was $50{\mu}m$.

• 한국자동차공학회논문집
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• 제15권1호
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• pp.89-98
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• 2007

Crashworthiness design is of special interest in automotive industry and in the transportation safety field to ensure the vehicle structural integrity and more importantly the occupant safety in the event of the crash. Front side assembly is one of the most important energy absorbing components in relating to the crashworthiness design of vehicle. The structure and shape of the front side assemblies are different depending on automakers. Thus, it is not easy to grab an insight on designer's intention when you glance at a new front side member without experiences. In this paper, we have performed the explicit nonlinear dynamic finite element analysis on the front side assembly of a passenger car to identify the mechanical roles of each part of the assembly and to enhance the absorbing energy from the viewpoint of reverse engineering.