• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.114-121
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• 2004

In order to investigate the corrosion fatigue characteristics in the weld of multi-pass welded A 106 Gr B steel pipe, corrosion fatigue tests were performed under the various stress ratios and 3.5 wt% NaCl solution at room temperature. The corrosion fatigue characteristic curves were represented using crack closure concept. The obtained results are as follows : when the load frequency is 1.0 Hz, the crack opening point is transited in the region of $K_{max}$=20∼32 MPaㆍ $m^{1}$2/. In the low stress intensity factor range, the crack opening point is higher than that in air. However, in the high stress intensity factor range, it is lower than that in air. In the cases of 0.1 Hz and 0.01 Hz, the crack opening point gradually decreases to $K_{min}$ with $K_{max}$ increase.rease.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.460-467
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• 2010

In housing units constructed recently in Korea, the length of ondol coil is different in each room, so the flow rate of hot water is adjusted by setting valve opening. If the flow rate is not appropriate for heating load, the room temperature seriously deviates from the set temperature range for comfort. In particular, too small valve opening can induce a noise by cavitation. In order to adjust the valve opening, two methods by zone area and a new method by return temperature rise were modelled and simulated using TRNSYS and EES. As a result, heating energy consumption during one week was the same on three methods, but the room temperature of the new method minimally deviated from the range of set temperature with a low possibility of noise.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.677-684
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• 2006

An ejector is a fluid transfer device to be used for mixing of fluids, maintaining vacuum, and overcoming a poor suction condition. To date, most ejectors have been made from the casting process. which is time-consuming and high-cost process. Therefore, a new production method of ejectors is desired if any. In this experimental study, we proposed a new type ejector manufactured from the commercial fitting materials and the welding process, which is equipped with an orifice type nozzle. The proposed ejector has a good integrity compared with the conventional ejector because the fittings have manufactured by forging and they have more strength than the casting materials. Furthermore we adopted a multi-opening orifice type nozzle for improving a suction capacity and compared with a single-opening orifice type nozzle. From the experimental results. we confirmed that the multi-opening nozzle had a food suction capacity than the single-opening nozzle and the proposed new type ejector showed higher vacuum than the conventional type ejector in non-load condition. These improved characteristics suggests that a new type ejector by using the commercial fittings opens the feasibility to be adopted in various industry fields and that the increased suction capacity can be achieved by altering the nozzle design of a conventional ejector.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.3
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• pp.317-322
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• 2011

This work has investigated the exhaust emissions such as Total Hydrocarbon (THC), Nitrogen Oxides(NOx), and Particulate Matter (PM) characteristics emitted from the tail-pipe of a continuously variable valve timing (CVVT) gasoline-fueled engine with different intake valve opening timings and injection pressures at the part load condition. Valve overlap period was varied from $40^{\circ}CA$ to $10^{\circ}CA$ and fuel injection pressure was increased from 3.5 bar to 5.0 bar. THC and NOx emissions decreased as intake valve opening timing was advanced regardless of fuel injection pressure. When the fuel was injected with the condition of 5.0 bar at all of valve overlap ranges, THC levels were reduced by 55%. NOx concentrations were diminished about 75% as valve overlap increased. PM size distributions were analyzed as bi-modal type of the nucleation and accumulation mode. Comparing with fuel injection pressures, PM emission levels were decreased at high pressure injection of 5.0 bar condition.

• Steel and Composite Structures
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• v.27 no.5
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• pp.555-566
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• 2018

A 1/3 composite cylindrical shell with a central rectangular opening was axially compressed experimentally, and its critical buckling load and displacement, and strains were measured. A finite element model (FEM) of the shell with Hashin failure criteria was established to analyze its buckling and post-buckling behaviors by nonlinear Newton-Raphson method. The geometric imperfection sensitivity and the effect of side supported conditions of the shell were investigated. It was found that the Newton-Raphson method can be used to analyze the buckling and post-buckling behaviors of the shell. The shell is not sensitive to initial geometric imperfection. And the support design of the shell by side stiffeners is a good way to obtain the critical buckling load and simplify the experimental fixture.

• Structural Engineering and Mechanics
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• v.19 no.3
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• pp.347-359
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• 2005

This paper attempts to develop the analytical model of estimating the fatigue damage using a linear elastic fracture mechanics method. The stress history on a welding member, when a truck passed over a bridge, was defined as a block loading and the crack closure theory was used. These theories explain the influence of a load on a structure. This study undertook an analysis of the stress range frequency considering both dead load stress and crack opening stress. A probability method applied to stress range frequency distribution and the probability distribution parameters of it was obtained by Maximum likelihood Method and Determinant. Monte Carlo Simulation which generates a probability variants (stress range) output failure block loadings. The probability distribution of failure block loadings was acquired by Maximum likelihood Method and Determinant. This can calculate the fatigue reliability preventing the fatigue failure of a welding member. The failure block loading divided by the average daily truck traffic is a predictive remaining life by a day. Fatigue reliability analysis was carried out for the welding member of the bottom flange of a cross beam and the vertical stiffener of a steel box bridge by the proposed model. Results showed that the primary factor effecting failure time was crack opening stress. It was important to decide the crack opening stress for using the proposed model. Also according to the 50% reliability and 90%, 99.9% failure times were indicated.

• Steel and Composite Structures
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• v.47 no.1
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• pp.103-117
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• 2023

This paper presents an investigation on the shear resistance of corrugated web steel beams (CWBs) with a circular web opening. A total of five specimens with different diameters of web openings were designed and tested with vertical load applied on the top flange at mid-span. The ultimate strengths, failure modes, and load versus middle displacement curves were obtained from the tests. Following the tests, numerical models of the CWBs were developed and validated against the test results. The influence of the web plate thickness, steel grade, opening diameter, and location on the shear strength of the CWBs was extensively investigated. An XGBoost machine learning model for shear resistance prediction was trained based on 256 CWB samples. The XGBoost model with optimal hyperparameters showed excellent accuracy and exceeded the accuracy of the available design equations. The effects of geometric parameters and material properties on the shear resistance were evaluated using the SHAP method.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.443-446
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• 2005

The Kaplan turbine model has been tested and analyzed. The blade angle and the guide vane opening of the turbine model were designed to be varied according to the best combination of guide vane and runner blade opening. When the changes in head and output were comparatively large, the efficiency drop were small, so the efficiency characteristics and stability of the entire operating condition were maintained in good condition. These results showed that the developed model in this study will be suitable for small hydro power stations with large changes in head and load.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1992-1996
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• 2007

The Kaplan turbine model has been tested and analized. The blade angle and the guide vane opening of the turbine model were designed to be varied according to the best combination of guide vane and runner blade opening. When the changes in head and output were comparatively large, the efficincy drop were small, so the efficiency characteristics and stability of the entire operating condition were maintained in good condition. These results showed that the developed model in this study will be suitable for small hydro power stations with large changes in head and load.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.7
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• pp.85-90
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• 2001

In order to apply the Leak-Before-Break(LBB)concept to nuclear piping, accurate estimation of J-integral and crack opening displacement(COD) is essential for complex loading, such as combined tension and bending. This paper proposes a new engineering method to estimate J-integral and the COD for circumferential through-wall cracked pipes subject to combined tension and bending loading. The proposed method to estimate the COD is validated against three published pipe test data, generated from a monotonically increasing bending load with a constant internal pressure, which shows excellent agreements.