• Journal of the Korean Society for Precision Engineering
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• v.19 no.3
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• pp.52-58
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• 2002

The purpose of condition monitoring and fault diagnosis is to detect faults occurring in machinery in order to improve the level of safety in plants and reduce operational and maintenance costs. The recognition performance is important not only to gain a high recognition rate bur a1so to minimize the diagnosis failures error rate by using off effective rejection module. We examined the problem of performance evaluation for the rejection scheme considering the accuracy of individual c1asses in order to increase the recognition performance. We use the Smith's method among the previous studies related to rejection method. Nearest neighbor classifier is used for classifying the machine conditions from the vibration signals. The experiment results for the performance evaluation of rejection show the modified optimum rejection method is superior to others.

• Geomechanics and Engineering
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• v.20 no.6
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• pp.497-503
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• 2020

In the Kingdom of Saudi Arabia, the shallower depth of the earth's crust is composed of loose dune or beach sand with soluble salts. The expansive behavior of salt bearing soil, fluctuation of ground water table and extreme environmental conditions offer a variety of geotechnical problems affecting safety and serviceability of the infrastructure built on it. Despite spending money, time and other resources on repair and rehabilitation, no significant attention is paid to explore the root causes of excessive differential settlement and cracking to these facilities. The scientific solution required to ensure safety and serviceability of the constructed infrastructure is to improve the strength and durability properties of the supporting ground. In this study, shredded plastic is employed as a low cost and locally available additive to improve strength characteristics of the desert sand. The study shows a remarkable increase in the shear strength and normal settlement of the soil. A seven (07) degree increase in angle of internal friction is achieved by adding 0.4 percent of the shredded plastic additive. The effect of different proportions and sizes of the plastic strips is also investigated to obtain optimum values. Such a long-lived solution will seek to reduce maintenance and repair costs of the infrastructure facilities laid on problematic soil along with reduction of environmental pollutants.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.739-744
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• 2009

Rail-pad is an important and readily replaceable component of a railway track, as it is the elastic layer between the rail and the sleeper. Characteristics and useful lifetime prediction of rail-pad was very important in design procedure to assure the safety and reliability. In this paper, the degradation of rail pad properties as a function of their in-service life is studied with a view of developing a technique for predicting the optimum period of track maintenance with regard to pad replacement. In order to investigate the useful lifetime, the accelerate test were carried out. Accelerated test results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the acceleration test, several useful lifetime prediction for rail-pads were proposed.

• Journal of Advanced Marine Engineering and Technology
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• v.19 no.4
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• pp.61-71
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• 1995

Nowadays the thin-walled metal bearing, which is made seperately from the bearing housing and has the ratio of wall thickness/bearing diameter being less than 1/30, are used in many newly developed large-sized slow speed diesel engines for the purpose of upgarding lubication performance and easy maintenance according to the trends of increasing output per cylinder and lowering engine speed. The type of this bearing has been used generally in many small-sized high speed engines applied for automobile, high speed craft and industrial power generation systems since 1950s. But the tranditional thick-walled bearings, whice are linned white metal on the bearing housing directly, have been installed on the large and slow speed engines until 1990s due to the easy manufacturing procedures. In this study we have calculated optimum dimensions of the metal bearing, fabricated special zigs for crush measurement, model test machine, 2 sets of specimens.(crosshead pin bearing, $\phi$818*552*20mm) for B & W 6S70MC(20, 940*88rpm), and evaluated metal constact phenomena of white metal, its friction coefficient, temparature rise through the model test and field performance test.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.9
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• pp.671-678
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• 2003

Spacer dampers maintain the constant gaps between each conductor in a bundle conductor-transmission line, and are installed at proper intervals to keep a line from all sorts of damages derived from the vibration energy caused by mechanical or electrical external factors. It is most important to embody a technology which considers difficulties of maintenance and repair, and has optimum elements in order to prevent accidents such as destruction by fire or the snapping of a wire by the effect of vibration phenomenon coming from transmission line. In the present thesis, therefore, the analysis of vibratory characteristics of spacer damper is set up by analytical methods such as the analysis of conductor motion's governing equation, the equation of spacer damper's motion, spacer damper-fastened wire's motion in a span, and the numerical analysis of finite difference method. Furthermore, the installation distance between spacer dampers was scrutinized by simulations of various vibration phenomena which change at any time as actual conditions do, and hereafter we will be able to analyze all kinds of vibration phenomena coming from a boltless spacer damper with 6 bundle conductor for 765 k V transmission line based on new analytical methods.

• Journal of Animal Environmental Science
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• v.1 no.1
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• pp.83-102
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• 1995

Composting is an ecologically sound method of recycling organic waste. Its advantages include the maintenance of soil fertility and improvement of soil physicochemical property. It is an essential part of the waste minimization. That is, composting should be included to increase the recycling rate up to more than 20%. To encourage composting of waste, it is necessary to develop some effective composters of small scale facilities and densely populated areas. For medium and large-size facilities, the optimum process should be selected. Technical counselling and support is desirable for small scale composters for urban residential and rural area. On the other hand, adequate amendment of relevant legislation should be followed to encourage composting. An example of unreasonable legislation is the current fertilizer management act. According to the regulation, the maximum allowable limit of lead in the compost is less than 150ppm, which is too strict. This limit should be increased to at least 300ppm, which is the observed level in most states in USA. At the same time, sound infrastructure should be established and decent publicity work should be achieved to accelerate composting activity. In this paper the desirable standard for some heavy metal concentration in the compost were suggested.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.503-508
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• 2003

Heating, Ventilation and hir Conditioning (HVAC) system in nuclear facility should be equipped and constructed more stable and allowable than that in common facility. The purpose of HVAC system is the maintenance of optimum working environment, the protection of worker against a contaminated air and the prevention of atmospheric contamination due to a outward ventilation, etc.. The basic scheme of a safety operation of nuclear facility is to prevent the atmospheric contamination even in low level. The adaptability of HVAC system should be taken into account in the design stage so that it is possible to modify the system which is in operation. In this study, the design requirements of HVAC system in nuclear facility and the HVAC systems in foreign countries are reviewed, and the results can be utilized in the design of HVAC system in nuclear facility.

• Journal of the Korean Society for Railway
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• v.13 no.3
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• pp.309-316
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• 2010

When the horizontal and vertical curves are superimposed in railway alignments, which affects the running stability, ride comfort, and track maintenance costs. However, when designing new lines or realigning existing ones, there are many cases of superimposition caused by the existing fixed points (bridge, tunnel, turnout, and catenary system, etc) on the conventional lines and undesirable impacts on the environment, etc. In this study, when the horizontal and vertical curves are superimposed, in order to optimize the horizontal curve in aspect of the ride comfort, the object function was developed and verified by vehicle dynamic analysis. Also, the solution algorithm for simplified evaluation method was presented.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.8
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• pp.556-562
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• 2008

The building HVAC systems have very different qualities of performance and durability with the superintendent's ability for management and maintenance. The poor management of these systems finally lead to the shortening of the life expectancy and result in the increase of operating costs and energy consumptions due to low efficiencies. This study presents an example of appropriate use of the LCC(Life Cycle Cost) analysis in a process of maintaining and repairing old HVAC equipments, by demonstrating the difference of optimal economic life, decrease of running cost, and energy consumption according to the management level of the HVAC equipments. But there are no reliable life expectancy and performance history data at present for optimal management of various building service equipments. Therefore, it is necessary to construct long-term database on operation results of them for more accurate and optimized LCC analysis.

• Journal of the Korean Society of Tobacco Science
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• v.8 no.1
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• pp.23-31
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• 1986

The water content, physical property and sensory of cigarette brands lave been studied from the view point of the individual and inner packages. It was found that the cigarettes had absorbed the moisture from alto more than 56% of a relative humidity (RH) and lost it under RH, 56%. The critical moisture contents for the optimum quality of cigarette maintenance were 7.7% through 14.595 in the range of equilibrium relative humidity (ERH) 52.2%-63.5%. The ERH at the initial moisture content of 12.1% showed 58.8% When cigarettes were storaged in 9095 of RH and 4$0^{\circ}C$, the shelf life of the Inner package was respectively shown 18.8 days In cellophane, 33.3 days In PET(25u), 69.8 days in OPP and 73.5 days in OPP film coated with PVDC. As shown above, the longest life time was found in the OPP film coated with PVDC. In the individual packages, the shelf life of packaging materials used above was significantly short in the same conditions as of the inner packages. Each shelf life of the individual packages was same In order comparing with that of the inner Packages.