• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.175-178
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• 1998

Tracings streamlines in global coordinate, especially with finite element mesh, requires much computation due to C0 continuity of velocity field. In this study, a new approach is presented for the determination of streamlines from velocity field obtained by FE analysis. It is shown that amount of calculation can be drastically reduced and boundary of element can be easily treated. The approach is applied to the problem of free surface of deforming workpieces in shape rolling.

• Nuclear Engineering and Technology
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• v.55 no.9
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• pp.3493-3505
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• 2023

Reactor containment buildings serve as the last barrier to prevent radioactive leakage due to accidents and their safety is crucial in overpressurization conditions. Thus, the Regulatory Guide (RG) 1.216 has mentioned the global strain as one of failure criteria in the free-field for cylindrical prestressed concrete containment vessels (PCCV) subject to internal pressure. However, there is a limit that RG 1.216 shows the free-field without the specific locations of failure criteria and also the global strain corresponding to only azimuth 135° has been mentioned in NUREG/CR-6685, regardless of the elevations of the structure. Therefore, in order to reevaluate the failure criteria of the 1:4 scaled PCCV, the high fidelity simulation model based on the experimental test was significantly validated in this study, and it was interesting to find that the experimental and numerical result was very close to each other. In addition, for the consideration of the material uncertainties, the Latin hypercube method was used as a statistical approach. Consequently, it was revealed that the radial displacements of various azimuth area such as 120°, 135°, 150°, 180° and 210° at elevations 4680 mm and 6,200 mm can represent as the global deformation at the free-field, obtained from the statistical approach.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.208-217
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• 1999

The present work describes the prediction method for the unsteady flow field and the acoustic pressure field of a ducted axial fan. The prediction method is comprised of time-marching free-wake method, acoustic analogy, and the Helmholtz-Kirchhoff BEM. The predicted sound signal of a rotor is similar to the experiment one. We assume that the rotor rotates with a constant angular velocity and the flow field around the rotor is incompressible and inviscid. Then, a time-marching free-wake method is used to model the fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson's method is used to predict the acoustic source. The newly developed Helmholtz-Kirchhoff BEM for thin body is used to calculate the sound field of the ducted fan. The ducted fan with 6 blades is analysed and the sound field around the duct is calculated.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.621-622
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• 2006

In this paper, we show some experimental results of binder-free WC sintered by Pulsed Electric Current Sintering (PECS) also known as Field Assisted Sintering Technology (FAST). These binder-free WC have extremely hardness and stiffness. However, these mechanical properties are dependent on the sintering condition, e.g., maximum temperature, applied pressure, etc. We show some relationship between mechanical properties and sintering condition to improve to sinter the binder-free WC.

• Korean Journal of Remote Sensing
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• v.17 no.4
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• pp.297-305
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• 2001

Ocean satellite altimetry-implied free-air gravity anomalies have had the shortest wavelengths removed during the processing to generate the optimal solution between multiple radar altimeter missions. ERS-1 168day mission altimetry was residualized to a reference geoid surface generated by integrating Anderson & Knudsen’s free-air gravity anomalies for the Barents Sea. The altimetry tracks were reduced and filtered to extract the shortest wavelengths (between 4 and 111 km) from both ascending and descending tracks, respectively. These data were recombined using existing quadrant-swapping techniques in the wavenumber domain to generate a correlated, high frequency gravity field related to the local geologic sources. This added-value surface adjusted the reference free-air gravity anomalies to better reflect features in the gravity field at a wavelength related to the distance between altimetry ground tracks.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.3939-3940
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• 2012

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.126-127
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• 2000

Resonance fluorescence is the manifestation of the interaction between the physical system under consideration and the vacuum-field fluctuation. The fluorescence spectrum provides such physical informations as the energy-level structure of the system, instabilities and relative populations of the energy levels, etc.. One of the typical fluorescence spectra is the Mollow triplet appearing when two-level atoms are driven by a strong coherent field in free space$^{(1)}$ . In the weak field limit, the singlet instead of the triplet is obtained with a reduced linewidth due to the squeezing of one quadrature phase of the induced atomic dipole$^{(2)}$ . On the other hand, when the atoms are put inside a cavity rather than in free space, a doublet spectrum due to the vacuum Rabi-splitting is achieved, showing clearly the coupling of atoms and the cavity in the single-quantum limit$^{(3)}$ . (omitted)

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.18 no.4
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• pp.305-316
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• 2014

The Hodge-Helmholtz decomposition splits a vector field into the unique sum of a divergence-free vector field (solenoidal part) and a gradient field (irrotational part). In a bounded domain, a boundary condition needs to be supplied to the decomposition. The decomposition with the non-penetration boundary condition is equivalent to solving the Poisson equation with the Neumann boundary condition. The Gibou-Min method is an application of the Poisson solver by Purvis and Burkhalter to the decomposition. Using the $L^2$-orthogonality between the error vector and the consistency, the convergence for approximating the divergence-free vector field was recently proved to be $O(h^{1.5})$ with step size h. In this work, we analyze the convergence of the irrotattional in the decomposition. To the end, we introduce a discrete version of the Poincare inequality, which leads to a proof of the O(h) convergence for the scalar variable of the gradient field in a domain with general intersection property.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.933-944
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• 1996

In this paper, two new techniques, the pattern filling and the refined flow field regeneration, based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible viscous flow with free surfaces. The gorerning equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The penalty and Newton-Raphson methods are used effectively for finite element formulation. The flow front surface and the volume inflow rate are calculated using the pattern filling technique to select an adequate pattern among five filling patterns at each quadrilateral control volume. By the refined flow field regeneration technique, the new flow field which renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. Using the new thchniques to be developed, the dam-breaking problem has been analyzed to predict flow phenomenon of fluid and the predicted front positions versus time have been compared with the reported experimental result.

• International Journal of Fluid Machinery and Systems
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• v.7 no.4
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• pp.174-182
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• 2014

The ultimate objective of this study is to develop a water turbine appropriate for low-head open channels to effectively utilize the unused hydropower energy of rivers and agricultural waterways. The application of a cross-flow runner to open channels as an undershot water turbine has been considered and, to this end, a significant simplification was attained by removing the turbine casing. However, the flow field of an undershot cross-flow water turbine possesses free surfaces, and, as a result, the water depth around the runner changes with variation in the rotational speed such that the flow field itself is significantly altered. Thus, clear understanding of the flow fields observed with free surfaces to improve the performance of this turbine is necessary. In this study, the performance of this turbine and the flow field were evaluated through experiments and numerical analysis. The particle image velocimetry technique was used for flow measurements. The experimental results reflecting the performance of this turbine and the flow field were consistent with numerical analysis. In addition, the flow fields at the inlet and outlet regions at the first and second stages of this water turbine were clarified.