• Horticultural Science & Technology
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• 제33권5호
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• pp.647-657
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• 2015

To investigate a method for calculation of the heating load for environmental designs of horticultural facilities, measurements of total heating load, infiltration rate, and floor heat flux in a large-scale plastic greenhouse were analyzed comparatively with the calculation results. Effects of ground heat exchange and infiltration loss on the greenhouse heating load were examined. The ranges of the indoor and outdoor temperatures were $13.3{\pm}1.2^{\circ}C$ and $-9.4{\sim}+7.2^{\circ}C$ respectively during the experimental period. It was confirmed that the outdoor temperatures were valid in the range of the design temperatures for the greenhouse heating design in Korea. Average infiltration rate of the experimental greenhouse measured by a gas tracer method was $0.245h^{-1}$. Applying a constant ventilation heat transfer coefficient to the covering area of the greenhouse was found to have a methodological problem in the case of various sizes of greenhouses. Thus, it was considered that the method of using the volume and the infiltration rate of greenhouses was reasonable for the infiltration loss. Floor heat flux measured in the center of the greenhouse tended to increase toward negative slightly according to the differences between indoor and outdoor temperature. By contrast, floor heat flux measured at the side of the greenhouse tended to increase greatly into plus according to the temperature differences. Based on the measured results, a new calculation method for ground heat exchange was developed by adopting the concept of heat loss through the perimeter of greenhouses. The developed method coincided closely with the experimental result. Average transmission heat loss was shown to be directly proportional to the differences between indoor and outdoor temperature, but the average overall heat transfer coefficient tended to decrease. Thus, in calculating the transmission heat loss, the overall heat transfer coefficient must be selected based on design conditions. The overall heat transfer coefficient of the experimental greenhouse averaged $2.73W{\cdot}m^{-2}{\cdot}C^{-1}$, which represents a 60% heat savings rate compared with plastic greenhouses with a single covering. The total heating load included, transmission heat loss of 84.7~95.4%, infiltration loss of 4.4~9.5%, and ground heat exchange of -0.2~+6.3%. The transmission heat loss accounted for larger proportions in groups with low differences between indoor and outdoor temperature, whereas infiltration heat loss played the larger role in groups with high temperature differences. Ground heat exchange could either heighten or lessen the heating load, depending on the difference between indoor and outdoor temperature. Therefore, the selection of a reference temperature difference is important. Since infiltration loss takes on greater importance than ground heat exchange, measures for lessening the infiltration loss are required to conserve energy.

• The Journal of Korean Association of Computer Education
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• 제9권1호
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• pp.107-118
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• 2006

Load redistribution algorithm is a critical factor in computer system. In a receiver-initiated load redistribution algorithm, receiver(underloaded processor) continues to send unnecessary request messages for load transfer until a sender(overloaded processor) is found while the system load is light. Therefore, it yields many problems such as low cpu utilization and system throughput because of inefficient inter-processor communications until the receiver receives an accept message from the sender in this environment. This paper presents an approach based on genetic algorithm(GA) for dynamic load redistribution including self-adjustable in heterogeneous distributed systems. In this scheme the processors to which the requests are sent off are determined by the proposed GA to decrease unnecessary request messages.

• Journal of Hydrogen and New Energy
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• 제35권4호
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• pp.370-376
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• 2024

Load variations reduce the lifespan of polymer electrolyte fuel cells (PEFCs). To analyze the impact of load variations on durability of PEFCs, two stacks were built and operated continuously for 400 hours, one under load variations and the other under constant current condition with the same energy output. Using the example model provided by Mathworks, we obtained load variation data for the experiments. The performance curves were measured every 100 hours and analyzed by current interruption method and electrochemical impedance spectroscopy. The degradation comparison shows a much larger decrease in performance under the load variation. The activation resistance, electrical resistance, and mass transfer resistance are all found to increase more.

• Journal of Power Electronics
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• 제19권3호
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• pp.637-644
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• 2019

Wireless power transfer (WPT) technology with various transfer mechanisms such as inductive coupling, magnetic resonance and capacitive coupling is being widely researched. Until now, power transfer efficiency (PTE) and power transfer capability (PTC) have been the primary concerns for designing and developing WPT systems. Therefore, a lot of studies have been documented to improve PTE and PTC. However, power consumption in the standby mode, also defined as the no-load mode, has been rarely studied. Recently, since the number of WPT products has been gradually increasing, it is necessary to develop techniques for reducing the standby power consumption of WPT systems. This paper investigates the standby power consumption of commercial WPT products. Moreover, a standby power reduction technique for WPT systems via magnetic resonance coupling (MRC) with a parallel resonance type resonator is proposed. To achieve a further standby power reduction, the voltage control of an AC/DC travel adapter is also adopted. The operational principles and characteristics are described and verified with simulation and experimental results. The proposed method greatly reduces the standby power consumption of a WPT system via MRC from 2.03 W to 0.19 W.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제29권2C호
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• pp.81-90
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• 2009

In this study the behavior of a steel pipe structure used as an auxiliary method was evaluated by the convergence-confinement method and load-transfer approach, and the result was compared with that of numerical approach and in-situ measured data. As calculated partially increased displacement of the installed pipe to obtain the tunnel displacement. A numerical analysis simulate well the general behavior of measured displacement of tunnel crown. Through this study, it was found that the proposed procedure produces conservative result so that it can be applied in preliminary design of the auxiliary method of tunnel face.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제25권7호
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• pp.511-515
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• 2012

A road energy harvester was designed and fabricated to convert mechanical energy from the vehicle load to electrical energy. The road energy harvester is composed of 24 piezoelectric cantilevers and a vehicle load transfer mechanism. Applying a vehicle load transfer mechanism rather than directly installing energy harvesters under roads decreases the area of road construction and allows more energy harvesters to be installed on the side of the road. The power generation amount with respect to the vehicular velocity change was assessed by installing the vehicle load transfer mechanism and the energy harvester in the form of speed bumps and underground. The energy harvester installed in a speed bump form generated power of 7.61 mW at the vehicular velocity of 20 km/h. Also, power generation of the energy harvester installed in the underground form was 63.9 mW at the vehicular velocity of 28 km/h. Although the number of piezoelectric cantilevers was reduced by 1/3 to 24 in comparison to the previous research results with 72 piezoelectric cantilevers, similar power generation characteristic value was obtained within the vehicular velocity of 20 km/h by altering the vehicle load transfer mechanism and cantilever vibration method.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제22권12호
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• pp.29-35
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• 2008

In this paper, The author present a load current feed-forward compensator by method that improve voltage controller of Step-down Chopper to get stable output voltage to sudden change of load current. To confirm the characteristics of a presented load current feed-forward compensator compared each transfer function of whole system that load current feed-forward compensator is added with transfer function of whole system that existent voltage controller is included using Mason gains formula in Root locus and Bode diagram. As a result the pole of system is improved, extreme point of the wave and system improves, and size of peak value and phase margin of break frequency in resonance frequency confirmed that is good. Therefore, presented control technique could confirm that reduce influence by perturbation and improves stationary state and dynamic characteristics in output of Step-down Chopper.

• Tunnel and Underground Space
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• 제12권2호
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• pp.107-114
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• 2002

It is the common practice to over design the reinforcement for the secondary tunnel lining due to the lack of rational insight into the ground loosening loads. and due to the conservative application of the empirical design methods. The main loads of the secondary lining are the ground Loosening loads and the ground water pressure, and the ground load is critical in the reinforcement design of the secondary lining in the case of drained tunnel. If the external load is absent around a tunnel, the reasons of the load far secondary tunnel lining are the deterioration of the primary supports such as shotcrete, steel rib, and rockbolts. Accordingly, the analysis method considering the ground-primary supports-secondary lining interaction should be required tar the rational design of the secondary tunnel lining. In this paper, the interaction was conceptually described by the simple mass-spring model and the load transfer from the ground and primary supports to the secondary lining is showed by the ground-primary supports-secondary lining reaction curves fur the theoretical solution of a circular tunnel. And also, the application of this proposed model to numerical analysis is verified in order to check the potential far the tunnel with the complex analysis conditions.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.2137-2142
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• 2003

One of the important performance metrics of the World Wide Web is how fast and precise a request from users will be serviced successfully. Shared Web Caching (SWC) is one of the techniques to improve the performance of the network system. In Shared Web Caching Systems, the key issue is on deciding when and where an item is cached, and also how to transfer the correct and reliable information to the users quickly. Such SWC distributes the items to the proxies which have sufficient capacity such as the processing time and the cache sizes. In this study, the Hot Spot Prediction Algorithm (HSPA) has been suggested to improve the consistent hashing algorithm in the point of the load balancing, hit rate with a shorter response time. This method predicts the popular hot spots using a prediction model. The hot spots have been patched to the proper proxies according to the load-balancing algorithm. Also a simulator is developed to utilize the suggested algorithm using PERL language. The computer simulation result proves the performance of the suggested algorithm. The suggested algorithm is tested using the consistent hashing in the point of the load balancing and the hit rate.

• Proceedings of the Korean Institute of Building Construction Conference
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• 한국건축시공학회 2012년도 춘계 학술논문 발표대회
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• pp.331-332
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• 2012

Structural steel has been used as a primary materials to columns and beams since 1960's in Korea with an advantages of excellent of load-bearing capacity and design flexibility, and faster construction. However, if the steel columns made of structural steel exposed to fire the load-bearing capacity is going down steadily and finally reach to collapse. Therefore, building regulation requires fire resistance according to building occupation, scales. The fire resistance can be evaluated two categories. One is prescriptive method that is based on building regulation, specification and so on and the other is performance-based fire engineering method. The latter can be designed based on scientific and engineering consequences. The easiest evaluation way using the fire engineering design is comparing to the limiting temperature and maximum temperature calculated based on heat transfer theory. If the limiting temperature of a column exceeds the maximum temperature of it, the column can carry the load during the fire. Therefore, the database of limiting temperature is very essential for evaluation of column. In this paper, to build the database of column made of rectangular hollow sections 8 fire tests with loading were conducted and the relation between the limiting temperature and the applied loads showed in reverse proportion.