• Geomechanics and Engineering
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• v.27 no.5
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• pp.527-535
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• 2021

The creep characteristics of rock is of great significance for the study of long-term stability of engineering, so it is necessary to carry out indoor creep test and creep model of rock. First of all, in different water-bearing state and different positive pressure conditions, the granite is graded loaded to conduct indoor shear creep test. Through the test, the shear creep characteristics of granite are obtained. According to the test results, the stress-strain isochronous curve is obtained, and then the long-term strength of granite under different conditions is determined. Then, the fractional-order calculus software element is introduced, and it is connected in series with the spring element and the nonlinear viscoplastic body considering the creep acceleration start time to form a nonlinear viscoplastic creep model with fewer elements and fewer parameters. Finally, based on the shear creep test data of granite, using the nonlinear curve fitting of Origin software and Levenberg-Marquardt optimization algorithm, the parameter fitting and comparative analysis of the nonlinear creep model are carried out. The results show that the test data and the model curve have a high degree of fitting, which further explains the rationality and applicability of the established nonlinear visco-elastoplastic creep model. The research in this paper can provide certain reference significance and reference value for the study of nonlinear creep model of rock in the future.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.223-233
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• 2003

Sand compaction pile (SCP) is one of the ground improvement techniques which are being used for not only accelerating consolidation but also increasing bearing capacity of loose sands or soft clay grounds. In this study, laboratory model tests and 3-D finite element analyses were performed to investigate the interaction between sand compaction piles and surrounding soft soils. Based on the results obtained, as the area replacement ratio increases, the stress concentration ratio increases at the pile point, the settlement decreases, and the relative displacement between column and soil also decreases. It is also found that numerical study is illustrated by good comparison with model test results, and the numerical analysis revealed slip effects which could not be specifically identified in the model tests.

• Tribology and Lubricants
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• v.31 no.2
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• pp.35-41
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• 2015

A water-pump located in the cooling area of a car circulates cooling water. A particular bearing element, known as a water-pump bearing, installed in the rotating part carries the entire load. The failure of this water-pump bearing has a direct impact on the failure of the automobile engine, and so securing its reliability is crucial. Several researchers have examined the design principles of the water-pump bearing, but there are no reports on the life characteristic of the bearing yet. Herein, we report the construction of test equipment to reproduce the spalling of the roller contact, which is the main failure mode of the chosen water-pump bearing. We chose the radial load as an accelerated stress factor and validated the failure mode by monitoring the surface defects. We conducted the accelerated life test after determining the accelerated stress level through a combination of finite element analysis and a preliminary test. In the life tests, we used an accelerometer to perform failure diagnosis. In the last stage of this study, we present a statistical reliability analysis. Thus, we fully estimated the shape parameter of the water-pump bearing, accelerating level on the load , and the lifetime (MTTF and B₁₀ life) under real use conditions, and finally proposed an interval estimation value considering the uncertainty of the estimated value.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.6
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• pp.177-185
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• 2018

There is a need to study dust separator screens with good drainage efficiency while effectively filtering suspended solids and other contaminants entering the intake pumping station, the drainage pumping station and the mediation pumping station, the cooling water inlet of the power plant, and the like. In this paper, Numerical studies were conducted for the optimal design of the dust separator screen using the Coanda effect. The shape of the dust separator screen is important, such as the right curvature radius $R_1$ at the top of the dust separator screen and the left curvature radius $R_2$ at the top, h is the height difference and shape between the screen and the accelerating plate, and ${\theta}$ is the inclination angle of the screen. A total of 4 shape factors were set and the effects of Coanda and drainage performance of each element were compared and analyzed, the optimum length and size of each shape element were derived by classifying the shape elements into direct and indirect influences. Finally, it was possible to effectively filter foreign matter by narrowing the screen spacing, and the drainage performance was analyzed and optimized through numerical studies of dust separator screen.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.1
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• pp.142-147
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• 2018

Private electrical facilities are judged whether it is suitable for the insulation aging condition of their incoming underground cables using DC leakage current test method. In the case where the service point of utility is the secondary side of cut out switch installed in the electric pole, there is a problem that it is difficult to separate the lightning arresters(LA) because of their high position of the pole. Therefore, the field test voltage is applied at value lower than DC 30 kV, which are stated in the inspection guideline. However, this test could reduced the insulation performance of the LA by accelerating the electrical stress of the metal oxide varistor element in the pre-breakdown region. In this study, we analyzed the relationship between the DC test voltage and the leakage current using the non-destructive DC high voltage equipment with leakage current measurement function. The results show that the leakage current increases sharply above the specified test voltage. As a consequence, it could be contributed to improve insulation aging inspection method by selecting the possible test area on the VI characteristic curve of the pre-breakdown area of the LA.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.1
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• pp.78-83
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• 2011

Phosphorus (P) which is required by all living plants and animals is an important input for economic crop and livestock production systems. Phosphorus containing compounds are essential for photosynthesis in plants, for energy transformations and for the activity of some hormones in both plants and animals. Loss of soil P to water can occur in particulate forms of P with eroded surface soil and in soluble forms in runoff, soil interflow, and deep leaching. The excessive losses of P from agricultural systems can degrade water quality of surface waters, resulting in accelerating eutrophication. Thus, P is often the limiting element and its control is of prime importance in reducing the accelerated eutrophication of surface waters. However, reserves of phosphate begin to run out, the impacts are likely be immense in terms of rising food prices, growing food insecurity. This paper reviews underappreciated resource as a key component of fertilizers and one of controversial pollutant in terms agronomy and environment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.4
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• pp.55-63
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• 2018

In recent years, with the growing interest in electric vehicles, the development of a Neighborhood Electronic Vehicle (NEV) made for urban driving is accelerating. Existing NEVs are set to ~0.3 - 0.35 with more emphasis on performance rather than minimizing air resistance. In this paper, a NEV with a streamlined car body is proposed. The shape of dolphins and sharks was applied to the car body to minimize the air resistance generated when driving. Also, the performance of the vehicle was estimated by calculating the traction force and the roll couple, etc. To check the drag coefficient of the car body, finite element analysis software (COMSOL Multiphysics) was used. The frame of the vehicle is divided into the forward and the rear parts. Carbon pipe is used for the frame by MIG welding. The car body of the vehicle was fabricated by forming carbon fiber. This study confirmed the general possibility of using NEVs through driving experiments.

• Korean Institute of Interior Design Journal
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• v.19 no.3
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• pp.22-29
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• 2010

Recent days, transition to ecological thought is being accelerating by environmental impact with a sustainable development. This symptom is no exception in architecture area. So is vernacular design affecting on modern architecture in many ways in terms of economical aspect and eco-friendly environment as well. Natural energy like solar power, environment, and terrestrial heat that applied in vernacular architecture is also widely accepted in name of 'sustainable energy' of which a design applied with ventilation and airing of natural wind is very useful & pragmatic in terms of economical reason. Accordingly, this study examined a relation between vernacular architecture and natural wind and compared it with traditional type and its feature of ventilation & airing. Ventilation & airing applied in the past can be divided into three categories: methods by convection, natural element, and architectural type. All these methods gave some pleasant felling indoors when there were no artificial energies. Even in modern age, such a ventilation & airing is being used with traditional type in different variety of materials, and it will be developed with modern technology without any extra cost in terms of sustainable expansion, and opened for further researches.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.6
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• pp.660-667
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• 2016

Maintaining proper tire air pressure is an essential element in ensuring vehicle safety. UHP Tires that boast of many safety features are increasing in the market. In particular, the development of "Self-Inflating Tire" technology is accelerating around the globe. Self-inflating tire refers to a technique for maintaining appropriate tire pressure. An internal regulator senses when tire inflation pressure has dropped below the set air pressure. The tire boosts air through the valve when rolling and compressed air enters into the tire. This procedure keeps the tire air pressure at an appropriate level and increases tire safety. Flow analysis of the internal tube is required to examine self-inflating tires. In this study, a method of tube flow analysis using the FSI Method is proposed. The valve system is also implemented to optimize the regulator and sensor.

• Geomechanics and Engineering
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• v.23 no.6
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• pp.535-546
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• 2020

The stress environment of deep rock masses is complex. Under the action of earthquakes or blasting, the strength and stability of anchored rock masses in fracture zones or faults are affected. To explore the variation in anchored rock masses under creep-fatigue loading, shear creep comparative testing of anchored marble specimens with or without fatigue loading is performed. Considering the damage variable of rock under fatigue loading, a rheological model is established to characterize the whole shear creep process of anchored rock masses under creep-fatigue loading. The results show that (1) the overall deformation of marble under creep-fatigue loading is larger than that under only shear creep loading, and the average deformation is increased by 18.3%. (2) By comparing the creep curves with and without fatigue loading, the two curves basically coincide when the first level stress is applied, and the two curves are stable with the increase in stress level. The results show that the strain difference among the specimens increases gradually in the steady-state stage and reaches the maximum at the fourth level. (3) The shear creep is described by considering the creep mechanical properties of anchored rock masses under fatigue loading. The accuracy of this creep-fatigue model is verified by laboratory tests, and the applicability of the model is illustrated by the fitting parameter R2. The proposed model provides a theoretical basis for the study of anchored rock masses under low-frequency earthquakes or blasting and new methods for the stability and reinforcement of rock masses.