• 한국소음진동공학회논문집
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• 제16권9호
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• pp.919-925
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• 2006

An accurate mathematical model for complex stiffness of the pneumatic spring would be necessary for an efficient design of a pneumatic spring used in vibration isolation tables for precision instruments such as optical devices or nano-scale equipments. A diaphragm, often employed for prevention of air leakage, plays a significant role of complex stiffness element as well as the pressurized air itself Therefore, effects of the diaphragm need to be included in the dynamic model for a more faithful description of dynamic behavior of pneumatic spring. But the complex stiffness of diaphragm is difficult to predict In an analytical way, since it is a rubber membrane of complicated shape in itself. Moreover, the diaphragm should be expandable in response to pressurization inside a chamber, which makes direct measurement of complex stiffness of diaphragm extremely difficult. In our earlier research, the complex stiffness of diaphragm was indirectly measured, which was just to eliminate the theoretical stiffness of pressurized air from the measured complex stiffness of the pneumatic spring. In order to reflect complex stiffness of inflated diaphragm on the total stiffness at the initial design or design improvement stage, however. it is required to be able to predict beforehand. In this paper, how to predict the complex stiffness of inflated rubber diaphragm by commercial FE codes (e.g. ABAQUS) will be discussed and the results will be compared with the indirectly measured values.

• 한국전산유체공학회지
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• 제5권1호
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• pp.1-7
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• 2000

In general, FDM(finite difference method) and FVM(finite volume method) are used for analyzing the fluid flow numerically. However it is difficult to apply them to problems involving complex geometries, multi-connected domains, and complex boundary conditions. On the contrary, FEM(finite element method) with coordinates transformation for the unstructured grid is effective for the complex geometries. Most of previous studies have used commercial codes such as KIVA or STAR-CD for the flow analyses in the engine cylinder, and these codes are mostly based on the FVM. In the present study, using the FEM for three-dimensional, unsteady, and incompressible Navier-Stokes equation, the velocity and pressure fields in the engine cylinder have been numerically analyzed. As a numerical algorithm, 4-step time-splitting method is used and ALE(arbitrary Lagrangian Eulerian) method is adopted for moving grids. In the Piston-Cylinder, the calculated results show good agreement in comparison with those by the FVM and the experimental results by the LDA.

• 소성∙가공
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• 제15권3호
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• pp.206-212
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• 2006

Design programs of tube-sheet for heat exchanger based on the related engineering society codes have been widely used. But it is not easy fer beginners to use the design programs. So we need to develop an easy program for design of tube-sheet for heat exchanger. This paper describes a developed design-program of tube-sheet fur heat exchanger. The developed program was coded on boiler theory and pressure vessel codes, provided by TEMA(Tubular Exchanger Manufactures Association) and ASME(American Society of Mechanical Engineers). Visual Basic, which is convenient for beginners to deal with, was used in the programming. Also a finite element analysis of tube-sheet for heat exchanger was carried to verify this developed program by using a commercial software, ANSYS. In the finite element analysis, tube and tube-sheet of heat exchanger were substituted by solid plate having equivalent properties for convenience of calculation. The thickness of tube-sheet obtained by the developed design-program was in good agreement with that of tube-sheet by FEA.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.844-849
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• 2006

Accurate modeling of complex dynamic stiffness of the pneumatic springs is crucial for an efficient design of vibration isolation tables for precision instruments such as optical devices or nano-technology equipments. Besides pressurized air itself, diaphragm made of rubber materials, essentially employed for prevention of air leakage, plays a significant contribution to the total complex stiffness. Therefore, effects of the diaphragm should be taken care of precisely. The complex stiffness of an inflated diaphragm is difficult to predict or measure, since it is always working together with the pressurized air. In our earlier research, the complex stiffness of a diaphragm was indirectly estimated simply by subtracting stiffness of the pressurized air from measurement of the total complex stiffness for a single chamber pneumatic spring. In order to reflect dynamic stiffness of inflated diaphragm on the total stiffness at the initial design or design improvement stage, however, it is required to be able to predict beforehand. In this presentation, how to predict the complex stiffness of inflated rubber diaphragm by commercial FE codes(e.g. ABAQUS) will be discussed and the results will be compared with the indirectly measured values.

• Computers and Concrete
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• 제3권4호
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• pp.197-212
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• 2006

Modeling of physically non-linear behavior becomes more and more important for the analysis of SFRC structures in practical applications. From this point of view we will present an effective, three-dimensional constitutive model for SFRC, that is also easy to implement in commercial finite element programs. Additionally, the finite element analysis should only require standard material parameters which can be gained easily from conventional experiments or which are specified in appropriate building codes. Another important point is attaining the material parameters from experimental data. The procedures to determine the material parameters proposed in appropriate codes seem to be only approximations and are unsuitable for precise structural analysis. Therefore a finite element analysis of the test itself is used to get the material parameters. This process is also denoted as inverse analysis. The efficiency of the proposed constitutive model is demonstrated on the basis of numerical examples and their comparison to experimental results. In the framework of material parameter identification the idea of a new, indirect tension testing procedure, the "Modified Tension Test", is adopted and extended to an easy-to-carry-out tension test for steel fiber reinforced concrete specimens.

• Nuclear Engineering and Technology
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• 제41권10호
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• pp.1347-1360
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• 2009

A multi-dimensional component for the thermal-hydraulic system analysis code, MARS, was developed for a more realistic three-dimensional analysis of nuclear systems. A three-dimensional and two-fluid model for a two-phase flow in Cartesian and cylindrical coordinates was employed. The governing equations and physical constitutive relationships were extended from those of a one-dimensional version. The numerical solution method adopted a semi-implicit and finite-difference method based on a staggered-grid mesh and a donor-cell scheme. The relevant length scale was very coarse compared to commercial computational fluid dynamics tools. Thus a simple Prandtl's mixing length turbulence model was applied to interpret the turbulent induced momentum and energy diffusivity. Non drag interfacial forces were not considered as in the general nuclear system codes. Several conceptual cases with analytic solutions were chosen and analyzed to assess the fundamental terms. RPI air-water and UPTF 7 tests were simulated and compared to the experimental data. The simulation results for the RPI air-water two-phase flow experiment showed good agreement with the measured void fraction. The simulation results for the UPTF downcomer test 7 were compared to the experiment data and the results from other multi-dimensional system codes for the ECC delivery flow.

• 한국해양공학회지
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• 제29권3호
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• pp.207-216
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• 2015

Amanifold is one of the essential subsea oil and gas production components to simplify the subsea production layout. It collects the production fluid from a couple of wellheads, transfers it to onshore or offshore storage platforms, and even accommodates water and gas injection flowlines. This paper presents the basic design procedure for a manifold frame structure with novel structural verification using in-house unity check codes. Loads and load cases for the design of an SIL 3 class-manifold are established from a survey of relevant industrial codes. The basic design of the manifold frame is developed based on simple load considerations such as the self weights of the manifold frame and pipeline system. In-house software with Eurocode 3 embedded, called INHA-SOLVER, makes it possible to carry out code checks on the yield and buckling unities. This paper finally proves that the new design of the manifold frame structure is effective to resist a permanent and environment load, and the in-house code is also adaptively combined with the commercial finite element code Nastran.

• 한국CDE학회논문집
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• 제8권2호
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• pp.115-121
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• 2003

A new Layered Manufacturing(LM) system, named PaperMill, is developed applying micro milling technology. A micro endmill(127 11m in diameter) is introduced as the cutter of build material. The selected build material for this system is an adhesive-coated paper roll which provides advantages such as good bonding between layers, machinability, and low material cost. A 3-axis CNC controller and three step-motors are used for the movement of X-Y-Z table of the system. For simplicity of the control of mechanism, the control system for feeding the paper roll is uncoupled from CNC controller. Two code converters are developed for the toolpath generation of the new LM system. The NC converter generates a set of NC codes for PaperMill using commercial CAM software while the SML converter generates an NC code from Quickslice's SML format. The NC codes generated from the converters consist of a series of profile data and trigger code for paper feeding. Two sample gears were fabricated to prove the concept of the system, which shown that the dimensional errors of the fabricated gears is under 3.4 percent.

• Nuclear Engineering and Technology
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• 제50권7호
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• pp.1088-1098
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• 2018

Kori unit #1, which is the first commercial nuclear power plant in Korea, was permanently shutdown in June 2017, and it is about to be decommissioned. Currently in Korea, researches on the decommissioning technology are actively conducted, but there are few researches on workers internal exposure to radioactive aerosol that is generated in the process of decommissioning nuclear power plants. As a result, the over-exposure of decommissioning workers is feared, and the optimal working time needs to be revised in consideration of radioactive aerosol. This study investigated the annual exposure limits of various countries, which can be used as an indicator in evaluating workers' internal exposure to radioactive aerosol during pipe cutting in the process of decommissioning nuclear power plants, and the growth and dynamics of aerosol. Also, to evaluate it, the authors compared/analyzed the cases of aerosol generated when activated pipes are cut in the process of nuclear power plants and the codes for evaluating internal exposure. The evaluation codes and analyzed data conform to ALARA, and they are believed to be used as an important indicator in deriving an optimal working time that does not excess the annual exposure limit.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3388-3400
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• 2023

Detailed analysis of the neutron pathway through matter inside the nuclear reactor core is exceedingly needed for safety and economic considerations. Due to the constant development of high-performance computing technologies, neutronics analysis using computer codes became more effective and efficient to perform sophisticated neutronics calculations. In this work, a commercial pressurized water reactor (PWR) presented by Virtual Environment for Reactor Applications (VERA) Core Physics Benchmark are modeled and simulated using a high-fidelity simulation of OpenMC code in terms of criticality and fuel pin power distribution. Various problems have been selected from VERA benchmark ranging from a simple two-dimension (2D) pin cell problem to a complex three dimension (3D) full core problem. The development of the code capabilities for reactor physics methods has been implemented to investigate the accuracy and performance of the OpenMC code against VERA SCALE codes. The results of OpenMC code exhibit excellent agreement with VERA results with maximum Root Mean Square Error (RMSE) values of less than 0.04% and 1.3% for the criticality eigenvalues and pin power distributions, respectively. This demonstrates the successful utilization of the OpenMC code as a simulation tool for a whole core analysis. Further works are undergoing on the accuracy of OpenMC simulations for the impact of different fuel types and burnup levels and the analysis of the transient behavior and coupled thermal hydraulic feedback.