• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.1974-1987
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• 2023

The load-following operation of small modular reactors (SMRs) requires accurate prediction of transient behaviors that can occur in the balance of plants (BOP) and the nuclear steam supply system (NSSS). However, 1-D thermal-hydraulics analysis codes developed for safety and performance analysis have conventionally excluded the BOP from the simulation by assuming ideal boundary conditions for the main steam and feed water (MS/FW) systems, i.e., an open loop. In this study, we introduced a lumped model of BOP fluid system and coupled it with NSSS without any ideal boundary conditions, i.e., in a closed loop. Various methods for coupling boundary conditions at MS/FW were tested to validate their combination in terms of minimizing numerical instability, which mainly arises from the coupled boundaries. The method exhibiting the best performance was selected and applied to a transient simulation of an integrated NSSS and BOP system of a SMART. For a transient event with core power change of 100-20-100%, the simulation exhibited numerical stability throughout the system without any significant perturbation of thermal-hydraulic parameters. Thus, the introduced boundary-condition coupling method and BOP fluid system model can expectedly be employed for the transient simulation and performance analysis of SMRs requiring daily load-following operations.

• Geomechanics and Engineering
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• v.25 no.1
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• pp.31-40
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• 2021

Injection grouting is one of the most common ground improvement practice to increase the strength and reduce the hydraulic conductivity of soils. Owing to the environmental concerns of conventional grout materials, such as cement-based or silicate-based materials, bio-inspired biogeotechnical approaches are considered to be new sustainable and environmentally friendly ground improvement methods. Biopolymers, which are excretory products from living organisms, have been shown to significantly reduce the hydraulic conductivity via pore-clogging and increase the strength of soils. To study the practical application of biopolymers for seepage and ground water control, in this study, we explored the injection capabilities of biopolymer-based grout materials in both linear aperture and particulate media (i.e., sand and glassbeads) considering different injection pressures, biopolymer concentrations, and flow channel geometries. The hydraulic conductivity control of a biopolymer-based grout material was evaluated after injection into sandy soil under confined boundary conditions. The results showed that the performance of xanthan gum injection was mainly affected by the injection pressure and pore geometry (e.g., porosity) inside the soil. Additionally, with an increase in the xanthan gum concentration, the injection efficiency diminished while the hydraulic conductivity reduction efficiency enhanced significantly. The results of this study provide the potential capabilities of injection grouting to be performed with biopolymer-based materials for field application.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.543-549
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• 2001

This research estimated stream discharges indirectly by hydraulic channel routing. Only stage data from three stage stations and river cross section data were used to estimate Manning roughness coefficients and to compute stream discharges. When the discharges were estimated a stage-stage set of conditions was used for upstream-downstream boundary conditions. The research used the data from the upper Mississippi River. The hydraulic channel routings were performed by DWOPER (operational dynamic wave model). The global optimization program of SCE-UA was used to improve the roughness coefficient estimation module of the modified Newton-Raphson method in DWOPER. The results from SCE-US were better. For the case study of a flood, most estimated discharges except a few show errors within 10%.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.5
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• pp.489-506
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• 2024

Excavation of tunnels below the groundwater table changes the hydraulic boundary conditions, causing flow towards the excavation face. Inflow into a tunnel is generally influenced by pre-excavation grouting, shotcrete lining, drainage system implementation, and the hydraulic deterioration of the drainage system. From the perspective of continuum theory, the groundwater inflow behavior due to excavation is very similar to the tunnel excavation behavior known as the convergence-confinement method. The groundwater inflow behavior due to tunnel excavation can be explained by the hydraulic convergence, while the behavior of shotcrete lining in limiting inflow can be inferred as hydraulic confinement. This study investigates the hydraulic convergence and confinement behavior using theoretical and numerical methods due to tunnelling. It is confirmed that the hydraulic convergence-confinement is exactly the same as the mechanical convergence-confinement concept. It is identified that the behavior is governed by the tunnel geometry, grout thickness and permeability, as well as the thickness and permeability of the support materials, such as shotcrete.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.69-84
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• 2020

Natural shoreline repeats its re-treatment and advance in response to the endlessly varying sea-conditions, and once severely eroded under stormy weather conditions, natural beaches are gradually recovered via a boundary layer streaming when swells are prevailing after storms cease. Our understanding of the boundary layer streaming over surf-zone often falls short despite its great engineering value, and here it should be noted that the most sediments available along the shore are supplied over the surf-zone. In this rationale, numerical simulation was implemented to investigate the hydraulic characteristics of boundary layer streaming over the surf zone in this study. In doing so, comprehensive numerical models made of Spatially filtered Navier-Stokes Eq., LES (Large Eddy Simulation), Dynamic Smagorinsky turbulence closure were used, and the effects of turbulence closure such as Dynamic Smagorinsky in LES and k-ε on the numerically simulated flow field were also investigated. Numerical results show that due to the intrinsic limits of k-ε turbulence model, numerically simulated flow velocity near the bottom based on k-ε model and wall function are over-predicted than the one using Dynamic Smagorinsky in LES. It is also shown that flow velocities near the bottom are faster than the one above the bottom which are relatively free from the presence of the bottom, complying the typical boundary layer streaming by Longuet-Higgins (1957), the spatial scope where boundary layer streaming are occurring is extended well into the surf zone as incoming waves are getting longer. These tendencies are plausible considering that it is the bottom friction that triggers a boundary layer streaming, and longer waves start to feel the bottom much faster than shorter waves.

• Journal of Soil and Groundwater Environment
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• v.9 no.4
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• pp.32-41
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• 2004

Analysis of water-level fluctuation due to goundwater-surface water interaction in coastal aquifers is carried out by numerical modeling. The conceptual model used in this study has a stream boundary and a tidal boundary that forms a right angle and the stream partially penetrates the aquifer. We analyzed the effect of each boundary and the simultaneous effect of the two boundary conditions. The area of influence caused by the stream boundary increased during the simulation, while the influence zone of the coastal boundary was relatively constant. The groundwater level near the zone where two boundaries meet may rise by the action of combined effect of the two boundaries or may not change by cancelling the effect of each boundary. Thereafter, care must be taken when hydraulic parameters are estimated using sinusoidal oscillations of hydraulic head in coastal aquifers. Sensitivity analysis is employed to develop insight into the controls on groundwater level fluctuations. In this study our analyses focused on the effect of conductance and the stream width to the aquifer nearby.

• Tunnel and Underground Space
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• v.15 no.2 s.55
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• pp.145-156
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• 2005

MODFLOW, 3-D finite difference code, is widely used to model groundwater flow and has been used to assess the effect of excavations on the groundwater system due to construction of subways and mountain tunnels. The results of numerical analysis depend on boundary conditions, initial conditions, conceptual models and hydrogeological properties. Therefore, its accuracy can only be enhanced using more realistic and field oriented input parameters. In this study, SA(simulated annealing) was used to integrate hydraulic conductivities from a few of injection tests with geophysical reference images. The realizations of hydraulic conductivity random field are obtained and then groundwater flows in each geostatistically equivalent media are analyzed with a numerical simulation. This approach can give probabilistic results of groundwater flow modeling considering the uncertainty of hydrogeological medium. In other words, this approach makes it possible to quantify the propagation of uncertainty of hydraulic conductivities into groundwater flow.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.35-39
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• 2009

In the hydraulic room of a forging press machine, a system which can detect and prevent risks at its early stage is needed because there may be a leakage due to the damage of the connection parts of the piping which can endanger human life and mechanical damage. In this paper, the system to automatically recognize a leakage of hydraulic fluid by the pan/tilt camera from a remote place is implemented. It finds the Minimum Boundary Rectangles(MBR) which are recognized with candidate leakage regions in the process of labeling and detects the proper leakage regions of hydraulic fluid with the width and height of MBRs and the area ratios of the MBRs and the candidate leakage regions. The experimental results show that the proposed system has been verified to detect the leakage regions accurately in various light conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.15-24
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• 1986

Pressure trasients must deal with safety problem of system. For identification of physical situation that can and method of limiting surges are essential consideration in sucessful design. The finite difference equation by method of characteristics are derived from the governing equation of unsteady flow in a pipe, and solved by using boundary condition derived. A computer program which can simulate general hydraulic system is developed by using finite difference equations and boundary conditions derived. The sumulated resulted by developed computer program are in fair agreement with experiment result.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.520-527
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• 2000

In the present study, the analytical approaches of vacuum consolidation with horizontal drains were proposed, For dissipating rapidly pore-water in hydraulic fills, vacuum consolidation method applied vacuum pressure in horizontal drains is developed. In the analytical approaches, the governing equation is based on two-dimensional finite strain consolidation theory and the boundary conditions of horizontal drains are considered in applying negative pore-water pressure occurred by vacuum pressure, Also, parametric studies to vacuum pressure and installation pattern of horizontal drains are carried out.