• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.962-967
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• 1991

A counter balance valve is used as one part of hydraulic motor brake system. The function of this valve is to protect over-run or free falling of inertia load. But occasionally the brake system with counter balance valve makes some undesirable problems such as pressure surges or vibrations. In this study, for the purpose of easy estimation about dynamic characteristics of hydraulic system including counter balance valve, precise formulation describing fluid dynamics and valve dynamics under various boundary conditions were made. Dynamic characteristics were analysed by numerical integration using Runge-Kutta method, because the equations in this circuit with counter balance valve contain various nonlinear terms. Propriety of this analysis method is verified by experiment. For the purpose of obtaining fundamental data for preventing instability, this study experimented the effects of the spool taper, spring constant, cylindrical choke. And we developed double acting brake system integrated counter balance valve.

• Nuclear Engineering and Technology
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• v.47 no.3
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• pp.284-292
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• 2015

A numerical calculation with the commercial computational fluid dynamics code CFX-14.0 was conducted for a test facility simulating the Canadian deuterium uranium moderator thermal-hydraulic. Two kinds of moderator thermal-hydraulic tests at Stern Laboratories Inc. were performed in the full geometric configuration of the Canadian deuterium uranium moderator circulating vessel, which is called a calandria tank, housing a matrix of horizontal rod bundles simulating calandria tubes. The first of these tests is the pressure drop measurement of a cross flow in the horizontal rod bundles. The other is the local temperature measurement on the cross section of the horizontal cylinder vessel simulating the calandria system. In the present study, the full geometric details of the calandria tank are incorporated in the grid generation of the computational domain to which the boundary conditions for each experiment are applied. The numerical solutions are reviewed and compared with the available test data.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1445-1451
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• 1994

To calculate the wave pressure acting on coastal structures under the design wave condition, it is often necessary to numerically reproduce the big standing wave profiles close to wave breaking condition. For this, the governing equation and all nonlinear terms occurring in boundary conditions should be effectively considered in the numerical wave profile. In particular, the velocity square term in the free surface boundary condition is very important. A boundary element method is applied here to calculate the standing wave profile with the velocity square term fully treated by Newton iterative method. In order to check the validity of the method, the numerical wave profiles are compared to ones calculated by the perturbation method, the Fourier approximation method and the hydraulic experiment.

• Journal of Coastal Disaster Prevention
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• v.1 no.1
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• pp.1-9
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• 2014

In order to examine the characteristics of tsunami run-up heights on impermeable/permeable slope, a numerical wave tank by upgrading LES-WASS-3D was used in this study. Then, the model were compared with existing hydraulic model test for its verification. The numerical results well reproduced experimental results of solitary wave deformation, propagation and run-up height under various conditions. Also, the numerical simulation with a slope boundary condition has been carried out to understand solitary wave run-up on impermeable/permeable slope. It is shown that the run-up heights on permeable slope is 52.64-63.2% smaller than those on the impermeable slope because of wave energy dissipation inside the porous media. In addition, it is revealed that the numerical results with slope boundary condition agreed well with experimental results in comparison with the results by using stair type boundary condition.

• Journal of the Korean Association of Geographic Information Studies
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• v.10 no.1
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• pp.124-135
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• 2007

The purpose of this study is to analyze the hydraulic behavior in a stream reach using SMS RMA-2 model with a series of dynamic boundary conditions of main stream and lateral flows simulated by WMS HEC-1 program. For the stream reach (10.5 km) between Gongdo and Pyeongtaek water level gauge stations of Anseongcheon, the model simulated two dimensional flow characteristics by applying dynamic flow conditions of rainfall frequencies of 50, 100, 500, and 1,000 years for the main stream and three tributaries. The temporal flow behavior successfully simulated and the results showed that the distribution of mean velocity and water level within the stream reach increased according to the increase of flow frequency. Especially, the flow velocity sensibly increased at the near downstream of lateral inflow as the width of main stream is narrower.

• Geomechanics and Engineering
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• v.20 no.2
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• pp.147-154
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• 2020

A novel approach for predicting lateral displacement caused by pile installation in anisotropic clay is presented, on the basis of the cylindrical and spherical cavities expansion theory. The K₀-based modified Cam-clay (K₀-MCC) model is adopted for the K₀-consolidated clay and the process of pile installation is taken as the cavity expansion problem in undrained condition. The radial displacement of plastic region is obtained by combining the cavity wall boundary and the elastic-plastic (EP) boundary conditions. The predicted equations of lateral displacement during single pile and multi-pile installation are proposed, and the hydraulic fracture problem in the vicinity of the pile tip is investigated. The comparison between the lateral displacement obtained from the presented approach and the measured data from Chai et al. (2005) is carried out and shows a good agreement. It is suggested that the presented approach is a useful tool for the design of soft subsoil improvement resulting from the pile installation.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2010.04a
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• pp.389-393
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• 2010

The Objective of this study was to develop a system for visualizing inundation area by using 1-D numerical model analyzing damage information such as inundation area, facilities, land usages, population, building, loads. In this study, we have reviewed hydraulic models to select a flood model for simulation of discharges, water depths and velocities. The study area is Namhan River from Youngwol to Paldang Dam which had a flood damage on upper and below regions of Chungju Dam by a storm event in 2006. At the first, we developed the DB system base on GIS thematic map, ortho images, cadastral maps to analyze flood damages and support decisions making. Changing the boundary conditions such as discharge at the gauging stations, flood simulations were performed and then damages were extracted from the databases information support system based on 1-D numerical hydraulic model, it is expected to be able to analyze flood damages and support a decision making for reduce flood relate damages. In the future, the system developed in this study could be applied for flood forecasting system of small scaled streams.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.3
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• pp.214-219
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• 1993

Counter balance valve is used as one part of hydraulic motor brake system. The function of this valve is to protect over-run or free falling of inertia load. But occasionally the brake system with counter balance valve makes some undesirable problems such as pressure surges or vibrations. These problems may hurt system safety and driver's conformability. Nevertheless, studies on dynamic characteristics of hydraulic system including counter balance valve are very rare, so further accumulation of research results are required. In this study, for the purpose of easy estimation about dynamic characteristics of hydraulic system including counter balance valve, precise formulation describing fluid dynamics and valve dynamics under various boundary conditions were made. The equations obtained in the preceding process include some parameters that must be got experimentally. Flow coefficients of valve and choke are the most significant ones among the parameters. So these parameters are obtained experimentally in this study, and experimental equations obtained from the experimental data were used for numerical calculation. The equations were analysed by numerical integration using Runge-Kutta method, because the equations contain various nonlinear terms. From the numerical analysis, it was verified that the dynamic response of counter balance valve and pressure variation at each elements can be estimated very easily. So the analysing method developed in this study enabled very easy estimating the relation between the performances of counter balance valve and various physical parameters related to the valve. Conclusively, it is said that the results obtained in this study can be used very usefully to develop a new type counter balance valve or to apply the valve to actual hydraulic system for various industrial equipments.

• Geomechanics and Engineering
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• v.28 no.2
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• pp.107-116
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• 2022

The steady state of unsaturated soil takes a long time to achieve. The soil seepage behaviours and hydraulic properties depend highly on the wetting/drying rate. It is observed that the soil-water characteristic curve (SWCC) is dependent on the wetting/drying rate, which is known as the dynamic effect. The dynamic effect apparently influences the scanning curves and will substantially affect the seepage behavior. However, the previous models commonly ignore the dynamic effect and cannot quantitatively describe the hysteresis scanning loops under dynamic conditions. In this study, a dynamic hysteresis model for SWCC is proposed considering the dynamic change of contact angle and the moving of the contact line. The drying contact angle under dynamic condition is smaller than that under static condition, while the wetting contact angle under dynamic condition is larger than that under static condition. The dynamic contact angle is expressed as a function of the saturation rate according to the Laplace equation. The model is given by a differential equation, in which the slope of the scanning curve is related to the slope of the boundary curve by means of contact angle. Empirical models can simulate the boundary curves. Given the two boundary curves, the scanning curve can be well predicted. In this model, only two parameters are introduced to describe the dynamic effect. They can be easily obtained from the experiment, which facilitates the calibration of the model. The proposed model is verified by the experimental data recorded in the literature and is proved to be more convenient and effective.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.41-46
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• 2008

After choosing twenty sluice culverts located at national rivers by detailed appearance evaluation, hydraulic response test and acoustic televiewer in addition to surface geophysical explorations were carried out to investigate the cavities which exist at the boundary of sluice culvert and ground. Tapping, GPR, 3-D resistivity surveys and acoustic televiewer imagery obtained successful results in limited conditions according to characteristics of the sites. On the other hand, hydraulic response test successfully detected cavity existing at the lower part of sluice culvert and its continuity. However, hydraulic response test can not supply the quantitative informations on the scale and the shape of cavity. Thus it is very important for accurate investigation to make comprehensive interpretation after supplying various surveys proper to site characteristics.