• Journal of the Korea Safety Management & Science
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• v.11 no.2
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• pp.95-101
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• 2009

The present study is to estimate the effect of wave height affecting at the front face of breakwater systems due to specification of submarine trench such as distance from breakwater to dredged area and width of dredge. The wave diffraction field, which is important hydraulic factor in the ocean, is considered to be two dimensional(2D) plane and the configuration of the submarine dredge on the sea bed designated by single horizontal long-rectangular pit system according to the various specific conditions of dredged locations. The numerical simulation is performed by using Green function based on the boundary integral equation and meshed at moving boundary conditions. The results of present numerical simulations are illustrated by applying the normal incidence. It is shown that the ratios of wave height at the front face of breakwater was varied by dependance of distant from breakwater to dredged area and width of dredge. It means that, when the navigation channel or pit breakwater is dredged on seabed, engineers have to consider the specification of dredge. This study can effectively be utilized for safety assessment to various breakwater systems in the ocean field and provided for safety construction of offshore structure.

• Journal of the Korea Society for Simulation
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• v.23 no.3
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• pp.33-40
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• 2014

Drifter is equipment which is hard to localize. Performance of prototype hasn't performed well compared to product of leading companies even though advanced foreign firm's product were dead copied. This study shows cases of approaching the factor which produces performance gap through drifter hydraulic analysis model which is core component of rock drill. Progression of procedure is following. 1) Securing reliability of the analysis model by comparing impact test result with analysis result. 2) Drawing a graph which indicates performance gap between prototype and drifter of advanced foreign firm by using analysis model. 3) Approaching the factor which produces performance gap with analysing variable of the analysis model. Software used for this analysis is SimulationX.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.117-120
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• 2008

Numerical simulations and experiment of a hydrodynamic and thermally developed turbulent flow through square ducts (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are conducted to investigate regionally averaged heat transfer and friction factors. Turbulent swirl flows having Reynolds numbers ranging from 8,900 to 29,000, a rib height-to-channel hydraulic diameter(e/D$_h$) of 0.067, and a length-to-hydraulic diameter(L/D$_h$) of 30, are considered. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape has 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Each wall is composed of isolated aluminum sections, and two cases of surface heating are set. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating conditions, and square ducts with twisted tape inserts plus interrupted ribs produces the best overall transfer performance.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.11 no.4
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• pp.28-34
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• 2015

The groundwater heat pump (GWHP) systems have great potential for heating-cooling system which use annual constant groundwater temperature for heat source. Generally, the performance of GWHP system significantly depends on the geological and hydraulic properties such as hydraulic conductivity, thermal conductivity, soil condition so on. Therefore, in order to use GWHP systems efficiently, it is necessary to analyze the effect of design factors on the system performance. However, there are a few researches on the optimum design method for the open-loop geothermal system. In this research, the design factor in the open-loop geothermal system was analyzed quantitatively for the optimal design method by using numerical simulation. As a result, it was found that the temperature change of heat source depends on the design factor.

• Journal of Drive and Control
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• v.19 no.1
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• pp.34-42
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• 2022

Hydrostatic transmission (HST) comprises rotary parts, shafts, valve plate, swashplate, and servo pistons. Ensuring structural stability of each part of an HST has a significant impact on product safety. In this study, the structural stability of HST in agricultural machinery and industrial vehicles was analyzed using ANSYS software. For conservative evaluation, high-pressure conditions (35.5 MPa and 2 MPa pilot pressure) were applied as load conditions. The number of grids used in the calculations ranged from 0.4 to 0.8 million depending on modeling requirements. Structural analysis was performed for essential parts and safety factor was analyzed. All major parts of HST had a safety factor of ≥ 1.5. Thus, they were judged to be structurally safe. This study provides important information for designing an HST system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.317-323
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• 2020

In this study, the correlations between flow rate, exhaust pressure, and droplet mean diameter with the shape factor of a water curtain nozzle were investigated. To analyze the flow coefficient and the distribution constant on the effects of the hydraulic diameter, five nozzles (D5W3, D5W6, D5W8, D4W6, and D7W6) were mocked up with a consideration of the internal diameter and width. The results showed that the flow coefficient increased in proportion to the constant 0.79 and 62.8 of the hydraulic diameters according to the diameter. As the nozzle width increased, the average droplet size decreased to the -0.235 exponential of the pressure. The average volume was reduced, in which the size distribution of the volume indeterminate decreased with increasing pressure for the same nozzle of the water-curtain. The distribution constants of droplet increased in proportion to the 0.258 exponential of the hydraulic diameter and 244.21. These results are expected to be useful to the design of pressure, flow meter, and average droplet size from a water curtain nozzle to predict the flow characteristics.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.6
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• pp.555-561
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• 2020

In this study, the applicability of Hunt's analytical solution for a two-layered leaky aquifer system, which was developed to estimate stream depletion due to the groundwater pumping of the upper shallow aquifer, was evaluated. The 5-year averaged stream depletions were estimated using Hunt's analytical solution for various combinations of hydraulic characteristic values such as transmissivity, storage coefficient of the two aquifers, interlayer leakage coefficient, stream-well distance, hydraulic conductivity of the streambed, and stream width. Through comparison with the numerical solution accurately simulated with a MODFLOW groundwater flow model, the analytical solution derived by regarding the stream width as a point was evaluated. It was found that the error in the stream depletion calculated by the analytical solution can be reduced to less than 0.05 when the stream-well distance is greater than the stream width or when the stream depletion factor (SDF) is more than about 3,000 days. In addition, when the streambed hydraulic conductivity is less than 1 m/d, the hydraulic diffusion coefficient of the lower aquifer layer is less than 100 ㎡/d, the hydraulic diffusion coefficient ratio of the upper and lower aquifer layers is 5 or more, and the leakage coefficient between the layers is less than 0.0004 m/d, the overall analytical solutions were overestimated compared with the numerical solutions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.963-971
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• 2000

Gerotor is a planar mechanism consisting of a rotor and lobes which form a closed space, namely a chamber. As active contact points between a rotor and lobes are subjected to very high contact stresses, wear in one or both of the rotor and lobe cannot be avoided. Therefore, in the design of Gerotor used in hydraulic motors a compromise between high torque output and contact stress is of great importance and a thorough analysis of design parameters should be conducted to achieve this compromise. In this study, a contact point is modelled as a linear spring in consideration of equivalent curvature to analyze the contact stress. As the contact stress calculation in this problem is a statically indeterminate type, a numerical iterative scheme has been adopted to obtain the solution. To fully understand the influence of design parameters on the contact stress, the relationship between pressure force, equivalent curvature, contact force and contact stress are analyzed. It is shown that the equivalent curvature of the contact point is a dominant factor that affects the maximum contact stress.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.3
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• pp.68-74
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• 1998

Performance and efficiency of deep seabed collector is a primary factor for feasibility of commercial deep ocean mining. The efficiency of manganese nodules collector depends on vehicle mobility relative to undulating seafloor and is attributed pickup head to keep altitude and elevation of it against seafloor. For this reason, motion control of pickup head relative to the changing deep-sea topography and other disturbances is of particular importance in design of pickup device. The concept of design axiom is applied to a pickup device of hybrid type in order to evaluate the concept design. Kinematic analysis conducted in absolute Cartesian coordinates gives position, velocity, and acceleration of the hydraulic cylinders which enable the pickup head to keep the preset optimal distance from seafloor. Inverse dynamic analysis provides the driving forces of hydraulic cylinders and the reaction forces at each joint. Design sensitivity analysis is performed in order to investigate the effects of possible design variables on the change of the maximum strokes of hydraulic cylinders. The direct differentiation method is used to obtain the design sensitivity coefficients.

• Journal of Applied Reliability
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• v.11 no.3
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• pp.235-244
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• 2011

Hydraulic hose assemblies deliver a fluid power in various oil pressure equipment such as construction machinery, automobile, aircraft, industrial machinery, machine tools and machinery for ships. Also, they are widely used as pipes in oil pressure circuit. When we estimate their lifetime, it is essential to conduct an accelerated life test by choosing the factor that suits the usage condition of the test object since traditional test method for estimating lifetime under the influence of various external factors incurs hardship in terms of time and expenses. The objective of this study is to propose an acceleration model that takes both temperature and pressure without flexing condition into consideration. The lifetime is estimated by applying the proposed temperature-nonthermal acceleration model to the test data. And we compare the proposed temperature-nonthermal acceleration model and the accelerated life equation suggested by John(1994).