• Journal of Power Electronics
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• v.3 no.3
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• pp.145-150
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• 2003

Reliability, availability, and cost have been the major concerns for photovoltaic hybrid systems since their beginning as primary sources for much critical applications like communication units and repeaters. This paper descnbes the performance of two hybrid systems, photovoltaic-battery, wind-turbine coupled with the public-grid (PVBWG) hybrid system and photovoltaic-battery, wind-turbine coupled With the diesel generator (PVBWD) hybrid system The systems are sized to power a typical 300W/48V de telecommunication load continuously throughout the year Such hybrid systems consist of subsystems, which in turn consist of components Failure of anyone of these components may cause failure of the entire system. The reliability and availability basics, and estimation procedure for the two proposals are introduced also in this paper. The PVBWG and PVBWD system configurations are shown with the relevant mean-time-between-faIlure (MTBF) and failure rate (${\lambda}$) of each component. The characteristics equations of the two systems are deduced as a function of operating hours and the percentage of sun and wind availabilities per day. The system probability failure as well as the reliability is estimated based on the fault tree analysis technique. The results show that, by using standard or normal components MTBF, the PVBWG is more reliable and the time of periodic maintenance period is more than one year especially in the rich sites of both sun and wind, but PVBWD competes else Also, in the first five years from the system installation, the system is quit reliable and may not require any maintenance. The results show also, as the sun and wind are available, as the system reliable and available.

• Smart Structures and Systems
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• v.6 no.2
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• pp.135-146
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• 2010

This paper presents the perspective of the Structural Mechanics program of the Air Force Office of Scientific Research (AFOSR) on the damage assessment of structures for the period 2006-2009 when the author was serving as Program Manager at AFOSR. It is found that damage assessment of structures plays a very important role in assuring the safety and operational readiness of US Air Force fleet. The current fleet has many aging aircraft, which poses a considerable challenge for the operators and maintainers. The nondestructive evaluation technology is rather mature and able to detect damage with considerable reliability during the periodic maintenance inspections. The emerging structural health monitoring methodology has great potential, because it will use on-board damage detection sensors and systems, will be able to offer on-demand structural health bulletins. Considerable fundamental and applied research is still needed to enable the development, implementation, and dissemination of structural health monitoring technology.

• Journal of the Korea Safety Management & Science
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• v.9 no.4
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• pp.121-127
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• 2007

CSP(Concurrent Spare Parts) is supplied with the procurement of new equipment or weapon system and is used to sustain the equipment without resupply during the initial coverage period. This study is concerned with a problem of determining the near optimal inventory level of the spare parts, especially Concurrent Spare Parts. For this, we utilize the mixed periodic and continuous review polices considering the CSP and (r,Q) Policies concurrently in a two-echelon distribution system. We propose the mathematical model to minimize the total cost which is composed with ordering cost, purchasing cost, holding cost, and stickout cost. If the mixed policy is compared to other policies(CSP, (r,Q)), the proposed methodology performs well and is best policy in the equipment maintenance expenses.

• Journal of the Korea Safety Management & Science
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• v.25 no.3
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• pp.31-36
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• 2023

The use of hanging scaffolding for exterior wall painting and cleaning in building construction and maintenance carries the inherent risk of fall accidents. While periodic rope replacement is crucial for preventing accidents resulting from rope breakage, current regulations lack specificity in determining appropriate disposal period for fiber ropes. This study analyzed the tensile strength of the most commonly used PP fiber ropes with different diameters (16 mm, 20 mm) in the domestic construction industry. Additionally, the effect of outdoor exposure was examined by measuring the tensile strength of new ropes and ropes exposing to outdoor conditions for 30 days and 90 days. The results showed that the new ropes and those exposed to outdoor for 30 days met the KS (Korean Standards) criteria for tensile strength. However, a significant decrease in tensile strength was observed in ropes exposed to outdoor for 90 days compared to both the new ropes and those exposed for 30 days. Furthermore, the ropes exposed for 90 days did not meet the KS criteria. These findings indicate the degradation of PP fiber ropes due to UV (Ultra Violet) radiation, highlighting the importance of considering this factor when determining the replacement period for fiber ropes used in scaffolding work.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.418-426
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• 2021

This study investigates the perception of radiation safety management in radiation generator manufacturing workers and medical institutions. The basic data obtained is further applied to improve active coping ability and safety levels. The knowledge and attitude practice score of radiation was found to be related to gender, age, marital status, occupation, position, current work period, total work period, radiation related work period, the manual available, defense facility maintenance, number of defense equipment, radiation safety education, special health examination, and recognition of radiation terms. In particular, the knowledge score of radiologists was highest among the radiation-related occupations (<0.05). Radiation safety management requires active defense endeavors to prevent radiation exposure, by both workers of radiation manufacturers and medical institutions. Moreover, institutional devices such as compliance with guidelines, periodic education, facility reinforcement, manual preparation, and special health checkups are required for efficient radiation safety management.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.46 no.1
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• pp.48-54
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• 2023

Guided missiles are a one-shot system that finishes their purpose after being used once, and due to the long-term storage until launch, the storage reliability is calculated during development, and performance is maintained through periodic inspections until the life cycle arrives. However, the reliability standards applied in the development of guided missiles were established by analyzing data accumulated by the United States during long-term operation in the country, and since they are different from our environment, the 00 guided missiles that have been deployed in the armed forces for more than 10 years under the premise that there is a difference from actual reliability. As a result of verifying the appropriateness of the current inspection cycle by analyzing the actual reliability of the missile, the necessity of changing the inspection period was derived because it was higher than the predicted reliability. It is proposed to build and utilize a lifespan management system that can systematically collect all data such as shooting and maintenance results by classification, and to establish a reliable reliability standard based on the accumulated data.

• Journal of Veterinary Clinics
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• v.14 no.2
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• pp.301-307
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• 1997

These studies were performed to provide some basic informations for developing an automatic system in dairy farming cattle in order that the farmers may easily and automatically detect the maintenance of pregnancy and the fact of abortion of the pregnant cows and also to find out the diseased animals with fever. As a method of automatical detection of the maintenance of pregnancy or the fact of abortion, weighing the pregnant cows was conducted from one month-pregnancy to the term using a digital balance. From the first to the 3rd month of pregnancy the body weight of dairy cows was slowly increased (less than 2% per month), then, relatively high increase (3.4% -4.3% per month) from the fourth to the seventh month followed by decrease (3.3%) in the 8th month and very low increase (0.8-0.9%) from the 9th month to the term were shown, resulting in increase of 128.8 kg (25.05%) of body weight to be compared with the first weight. More than 107, increase of body weight to be compared with the first month-weight was denoted from the 61th month of pregnancy and more than 20% increase from the 7th or the 8th month of pregnancy as wells consequently it was presumed that detection of the maintenance of pregnancy is possible from the 4th or the 5th month of pregnancy. It was possible to diagnose a cow aborted at the 6th month by continual weighing the cow from the 1st month of pregnancy. The calved cows showed considerably higher decrease of body weight even in the third week after parturition (p<0.01)to be compared with the body weight near to the term (81.8-102.0 kg, 14-16% decrease). During the same period of 8months, the pregnant cows gained 127.4 kg (24.78% increase), whereas the non-pregnant cows gained 33.0 kg (0.71% increase) to be compared with the first weight showing considerably higher increase of body weight gain in the pregnant cows than the non-pregnant cows (p<0.01). The statistics of body temperatures of dairy cattle were collected from three clinics including the Teaching Hospital of Chonbuk University and the diseases were classified simply by the major symptoms manifested, denoting the highest temperature in respiratory disease ($39.8{\circ}C$) and the lowest in alimentary disease ($39.6{\circ} C$). These informations of body temperatures were expected to be of value for early and automatical detection of the diseased animals with fever when automatic machinery would be established. The results of periodic weighing the body weight of pregnant cows while milking were also expected to be of great use for the farmers to detect the maintenance of pregnancy and the fact of abortion when the automatic system is established in the near future.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.589-597
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• 2010

Steel structures have a higher probability of being damaged by fatigue than by other causes of deterioration. As such, their maintenance to prevent fatigue damage is essential to sustain their safety and performance during their service period. In their maintenance, the current state of their fatigue cracks must be assessed to determine appropriate reinforcement methods and the suitable time intervals of periodic inspections when fatigue cracks are detected. Determining the crack growth rate is a successful method of predicting fractures, but it requires technical knowledge on fracture mechanics and experience in numerical methods and software for finite element analysis. In this study, a fatigue crack growth test on through-thickness cracked steel plates was conducted to assess the crack growth rate without superior technical knowledge and experience. The relationship between the Crack Opening Displacement (COD) and the crack growth rate was found in relatively long fatigue cracks.

• The Journal of the Korean dental association
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• v.47 no.9
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• pp.585-595
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• 2009

Purpose : The aim of this study was to compare surgical complications between simple implant placement and implant placement combined with complicated surgical procedures. We also evaluated prosthetic complications according to the specific types of prosthesis. Material and Method : A retrospective analysis of dental chart of patients who was performed implant therapy during the period from June 2003 to December 2005 was carried out. This study was performed on 408 patients (208 male, 200 female). In addition, 1671 implants were performed. Based on their medical record and radiographs, the authors evaluated surgical and prosthetic complications, surgical procedures accompanied at the time of implant, risk factors of implant failure etc. Result : Surgical complications were developed on 358 implants(21.4% on total placed implants) and wound dehiscence was most prevalent complication. On maxillary posterior area, surgical complications developed more frequently on implants with major surgery and showed a significant difference. And complication rate of implants accompanied with GBR was higher than that of simple implants placement and also showed significant difference. The implant supported prosthesis showed no statistical difference in the occurrence of complications according to the types of prosthesis, and food retention was the most common post-prosthetic complication. Also we speculated that length and width of implant showed significant correlation to the failure of implant primary osseointegration. Conclusion : Based on the result, clinician should provide more careful maintenance for patients with implant placement accompanied by complicated surgical procedure. And periodic maintenance for the patient is requested for long-term survival of implant therapy.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.3
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• pp.87-94
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• 2007

A structural dynamic analysis can be divided into a time domain analysis and a frequency domain analysis. The time domain analysis makes use of a direct integration method or a mode superposition method and the frequency domain analysis applies a DFT method. Generally the DFT method is more effective method in case of calculating response of periodic excitation. But in case of transient excitation exact solution can not be acquired. So, by modifying the response or increasing the period accuracy of solution can be enhanced. Accordingly this study analyzed dynamic responses of structures under aperiodic moving load in time domain and frequence domain. Consequently it is concluded that exact solution would be get enough using DFT method by increasing the duration of free vibration or modifying the dynamic response.