• Journal of Korean Association for Spatial Structures
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• v.14 no.1
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• pp.77-84
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• 2014

Simple 3, 10, and 30-story buildings with a nonstructural element which is located at roof or near the middle of the building height are selected. Based on 2009 Korean Building Code, the seismic design force applied at the nonstructural element is evaluated. Response spectrum analysis is conducted with the design response acceleration spectrum of 2009 Korean Building Code and the analytical response is compared with the seismic design force from the Code. Furthermore, an artificial earthquake based on Korean design response acceleration spectrum and the 50% intensity of El Centro earthquake, which can be considered as the maximum future earthquake possibly occurring in Korea, are selected to conduct time history analysis. When the period of the nonstructural element is shorter than 0.06 second or longer than that of the 1st period of each building, the Code equations of seismic design force for nonstructural element seems to be appropriate. However, the period of the nonstructural element is close to the one of the building's higher mode periods including the 1st period, seismic force of the nonstructural element might exceed the Code specified seismic design force.

• Journal of Radiation Protection and Research
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• v.29 no.1
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• pp.41-48
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• 2004

A safety assessment code, called SAGE (Safety Assessment Groundwater Evaluation), has been developed to describe post-closure radionuclide releases and potential radiological doses for low- and intermediate-level radioactive waste (LILW) disposal in an engineered vault facility in Korea. The conceptual model implemented in the code is focused on the release of radionuclide from a gradually degrading engineered barrier system to an underlying unsaturated zone, thence to a saturated groundwater zone. The radionuclide transport equations are solved by spatially discretizing the disposal system into a series of compartments. Mass transfer between compartments is by diffusion/dispersion and advection. In all compartments, radionuclides ate decayed either as a single-member chain or as multi-member chains. The biosphere is represented as a set of steady-state, radionuclide-specific pathway dose conversion factors that are multiplied by the appropriate release rate from the far field for each pathway. The code has the capability to treat input parameters either deterministically or probabilistically. Parameter input is achieved through a user-friendly Graphical User Interface. An application is presented, which is compared against safety assessment results from the other computer codes, to benchmark the reliability of system-level conceptual modeling of the code.

• Magazine of the Korea Concrete Institute
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• v.9 no.4
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• pp.167-176
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• 1997

The current study is a part of series of research about the evaluation method of the unbonded tendon stress in prestressed concrete member at flexural failure. As the first part. previous design equations were examined in oder to find whether any modifications may be needed. A total of 167 experimental results tested for more than 40 years were gathered to build D/B and then previous proposed and codified equations were evaluated with the experimental relsults. The ACI Code equation and Naaman, Harajli, and Chakrabarti's equations were chosen for the purpose of examination. Then, the followings were obtained from the analytical examination. It is desirable to compute the tendon stress with the member analysis method instead of the sectional analysis method which has been used in the current ACI Code. The tendon stress may also be influenced significantly by the amount of ordinary bonded reinforcements and the loading types. And the current ACI Code overestimated the effect of span/depth ratio. As results, it was concluded that the revision of the ACi Code equation should be considered positively. Then, a new design has to be proposed with the reasonable and comprehensive investigation about influential factors on the tendon stress variation.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.57-65
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• 2011

Both shear and torsional moments apply shear stresses on cross-section of a member, which need to be considered in the design. But in the current Korean Building Code, the design equations for shear and torsional moments are expressed in terms of the sectional strength with different units, causing figures to be drawn separately in two axes. If the design equations are expressed in terms of stresses, then the stresses of shear and torsional moments can be added, allowing figures to be drawn in one axis for easy recognition of the design procedure and the final design results. Moreover, the current code's design equations for shear and torsional moments are considered separately with the intention of summing the area of stirrups with respect to unit length for shear moment ($A_{\upsilon}/s$) and torsional moment ($2A_t/s$). Since the size or type of vertical stirrups are predetermined in the design process, the design equations are expressed in terms of the spacing of stirrups rather than the $A_{\upsilon}/s$ and $2A_t/s$ terms, clarifying various design steps and a design process.

• Journal of the Korea Institute of Building Construction
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• v.14 no.4
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• pp.336-342
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• 2014

Shear strengths of reinforced high strength concrete beams without web reinforcement are studied with experimental analysis of 10 specimen with 2.4 shear span-to-depth ratio (a/d) beams for 4 stages of concrete compressive stength over 60MPa comparing ultimate loads and shear stresses of ACI363R and KCI code equations. Expecially, concrete compressive strengths used in shear design were essentially limited to 10,000 psi (69MPa) by ACI363R and KCI Code. The modified Code equation's shear stresses of the specimen without the limit are compared with test results. The comparison between the modified exist Code equations results and test results are expected to show an available scope to apply in construction field and to give considerations of design and contraction.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2218-2229
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• 2006

A conservative finite-volume numerical method for unstructured grids with the cell-centered method has been developed for computing flow and heat transfer by combining the attractive features of the existing pressure-based procedures with the advances made in unstructured grid techniques. This method uses an integral form of governing equations for arbitrary convex polyhedra. Care is taken in the discretization and solution procedure to avoid formulations that are cell-shape-specific. A collocated variable arrangement formulation is developed, i.e. all dependent variables such as pressure and velocity are stored at cell centers. For both convective and diffusive fluxes the forms superior to both accuracy and stability are particularly adopted and formulated through a systematic study on the existing approximation ones. Gradients required for the evaluation of diffusion fluxes and for second-order-accurate convective operators are computed by using a linear reconstruction based on the divergence theorem. Momentum interpolation is used to prevent the pressure checkerboarding and a segregated solution strategy is adopted to minimize the storage requirements with the pressure-velocity coupling by the SIMPLE algorithm. An algebraic solver using iterative preconditioned conjugate gradient method is used for the solution of linearized equations. The flow analysis code (PowerCFD) developed by the present method is evaluated for its application to several 2-D structured-mesh benchmark problems using a variety of unstructured quadrilateral and triangular meshes. The present flow analysis code by using unstructured grids with the cell-centered method clearly demonstrate the same accuracy and robustness as that for a typical structured mesh.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.307-316
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• 2012

Numerical simulations of 3D aircraft configurations are performed in order to understand the effects of turbulence models on the prediction of aircraft's aerodynamic characteristics. An in-house CFD code that solves 3D RANS equations and two-equation turbulence model equations are used. The code applies Roe's approximated Riemann solver and an AF-ADI scheme. Van Leer's MUSCL extrapolation with van Albada's limiter is also adopted. Various versions of Menter's $k-{\omega}$ SST turbulence models as well as Coakley's $q-{\omega}$ model are incorporated into the CFD code. Menter's $k-{\omega}$ SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared with computational results from the $3^{rd}$ AIAA CFD Drag Prediction Workshop. Numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared with computational results of the $2^{nd}$ AIAA CFD Drag Prediction Workshop. Aerodynamic characteristics as well as flow features are scrutinized with respect to the turbulence models. The results obtained from each simulation incorporating Menter's $k-{\omega}$ SST turbulence model variations are compared with one another.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.527-534
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• 2002

In this paper, efficiency in the acquisition of the PN code of the DS/CDMA system was analyzed by using the Nakagami-m probability density function that can model diverse fading channels. The system considers the fading environment that inevitably exists in the mobile communications channel environment. To analyze the efficiency of the system, the equations related to detection probability PD and false alarm probability PFA required for the acquisition of the PN code were induced by using the Nakagami-m probability density function. They were verified through simulation. For the DS/CDMA system an adaptive serial search technique was applied to acquire the PN code. To correct phase error, the equations related to detection probability PD and false alarm probability PFA that influence the time to acquire codes were induced after adding the PLL to each branch of the Rake Receiver. By using an induced equation, detection probability PD and false alarm probability PFA were verified through simulation.

• Nuclear Engineering and Technology
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• v.41 no.7
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• pp.885-892
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• 2009

This manuscript will discuss a numerical method where the six equations of two-phase flow, the solid heat conduction equations, and the two equations that describe neutron diffusion and precursor concentration are solved together in a tightly coupled, nonlinear fashion for a simplified model of a nuclear reactor core. This approach has two important advantages. The first advantage is a higher level of accuracy. Because the equations are solved together in a single nonlinear system, the solution is more accurate than the traditional "operator split" approach where the two-phase flow equations are solved first, the heat conduction is solved second and the neutron diffusion is solved third, limiting the temporal accuracy to $1^{st}$ order because the nonlinear coupling between the physics is handled explicitly. The second advantage of the method described in this manuscript is that the time step control in the fully implicit system can be based on the timescale of the solution rather than a stability-based time step restriction like the material Courant limit required of operator-split methods. In this work, a pilot code was used which employs this tightly coupled, fully implicit method to simulate a reactor core. Results are presented from a simulated control rod movement which show $2^{nd}$ order accuracy in time. Also described in this paper is a simulated rod ejection demonstrating how the fastest timescale of the problem can change between the state variables of neutronics, conduction and two-phase flow during the course of a transient.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2696-2701
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• 2007

For the analysis of a two-phase flow, the interaction between two phases such as the interfacial momentum or heat transfer is proportional to the interfacial area. So the interfacial area concentration (IAC) is one of the most important parameters governing the behavior of each phase. This study focuses on the development of a computational fluid dynamics (CFD) code for investigating a boiling flow with a one-group IAC transport equation. It was based on the two-fluid model and governing equations were calculated by SMAC algorithm. For checking the robustness of the developed code, the experiment of a subcooled boiling in a vertical annulus channel was analyzed to validate the capability of the IAC transport equation. As the results, the developed code was confirmed to have the capability in predicting multi-dimensional phenomena of vapor generation and propagation in a subcooled boiling.