• Journal of Magnetics
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• v.16 no.3
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• pp.240-245
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• 2011

A new hybrid ON/OFF method is presented for the fast solution of electromagnetic inverse problems in high frequency domains. The proposed method utilizes both topological sensitivity (TS) and material sensitivity (MS) to update material properties in unit design cells. MS provides smooth design space and stable convergence, while TS enables sudden changes of material distribution when MS slows down. This combination of two sensitivities enables a reduction in total computation time. The TS and MS analyses are based on a variational approach and an adjoint variable method (AVM), which permits direct calculation of both sensitivity values from field solutions of the primary and adjoint systems. Investigation of the formulations of TS and MS reveals that they have similar forms, and implementation of the hybrid ON/OFF method that uses both sensitivities can be achieved by one optimization module. The proposed method is applied to dielectric material reconstruction problems, and the results show the feasibility and effectiveness of the method.

• International Journal of Automotive Technology
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• v.3 no.1
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• pp.33-40
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• 2002

Increasingly stringent emission regulations of EU and CARB (California Air resource Board) require mandatory OBD (On Board Diagnostics) far the catalytic converters of a vehicle. It demands that MIL(Malfunction Indication Light) should be tuned on to inform the driver of catalytic converter failures. Currently dual oxygen sensor method Is widely used for the converter OBD. However, since it works only alter converter light-off, it has a serious limitation when applied to TLEV or more stringent emission regulations where more than 85% of total emission is coming out before converter light-off. In addition, a recent development in catalyst material. coating technology and additive catalysts leads to a much improved OSC (Oxygen Storage Capacity) after converter light-off, current methods are very difficult to determine levels of converter aging. Therefore, it is desired to develop an OSC detecting method before converter light-off to diagnose converter failures with higher reliability. In this study, OSCs of converters are measured by an absolute measuring method and a dynamic measuring method, and some of fundamental ideas are suggested about converter OBD before converter light-off. The converters are aged with two different aging methods; those are a furnace aging and an engine bench aging: to represent aging conditions in actual field applications. Dual oxygen sensor method at the lower temperature than light-off is also studied at a model gas bench with the converters. It is fecund that there is a certain point in temperature lower than light-off where difference due to aging level becomes maximum, thus a proper dynamic method to effectively monitor catalytic converters could be implemented fur the range lower than light-off temperatures. With this result, the aging level of converters is examined at an engine bench.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.1
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• pp.13-17
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• 2006

In this paper, the RCF(Resistive Companion Form) analysis method which is used to analyze small signal stability problems of non-continuous systems including switching devices. The RCF analysis method is mathematically rigorous and computes eigenvalue of the system periodic transition matrix based on discrete system analysis method. As an effect of switching operations, the eigenvalues of the systems are changed and newly unstable oscillation modes may be occurred. As an illustrating example, the oscillation modes of the system with different switching time intervals are computed exactly by the RCF analysis method and the results show that ON/OFF time intervals of switching equipments are important factors to make the system stable or unstable. This result shows that the RCF analysis method is very powerful to analyze small signal stability problems of power systems including switching devices such as FACTS equipments.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.5
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• pp.534-541
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• 2007

This paper suggests the mathematical method for the estimation of the required engine output for WIG crafts. The engine size of a WIG craft Is a key parameter in the design stage, because WIGs should overcome the hump drag during the take-off. Therefore, it is very important for a WIG designer to estimate required power and state change during take-off. The mathematical method was developed based on the steady planing state model of a planing boat. Through numerical calculations on various take-off states, it was found that the suggested method could give reasonable estimation of required power and state change during take-off.

• 한국전기화학회:학술대회논문집
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• 2005.07a
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• pp.261-264
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• 2005

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.109-116
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• 1998

This paper is concerned with effective operating method of pneumatic on-off valves for improving position control accuracy, valve life-time and position settling time using modified pulse width modulation with dead-zone (MPWMD). The pneumatic system using on-off valves has advantage of simple construction and low cost compared with a system with servo-valves. The performance of the proposed control method is investigated experimentally for the position control of a pneumatic cylinder using on-off valves. Experimental results show that the proposed algorithm for valve operation can be used to obtain fast and accurate position control compared to the conventional PWMD algorithm. It is also shown that the use of the proposed MPWMD algorithm for the position control significantly reduces the number of valve switching and noise.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.493-502
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• 2002

During the defrosting process, the temperature in the cabinet of a showcase becomes high as compared to the setting point, which is not desirable for stored foods or materials. It is necessary to develop a more efficient defrosting method to prevent large temperature fluctuation. In this study, the performance of a showcase refrigeration system with three evaporators is investigated by employing a hot-gas bypass defrosting technology in the system under frosting and defrosting conditions. The operating characteristics are compared with those for the on-off defrosting method that has been widely used in current products. As a result, the hot-gas bypass defrosting method shows higher refrigerating capacity and less temperature fluctuation than the on-off method under frosting/defrosting conditions, while the power input is relatively high for the hot-gas bypass method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.820-825
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• 1996

This paper is concerned with effective operating method of pneumatic on-off valves for improving position control accuracy, valve life-time and position settling time using modified pulse width modulation with dead-zone. The pneumatic system using on-off valves studied in this paper has advantage of simple construction and low cost compared with a system with servo-valves. The performance of proposed control system is investigated experimentally for the position control of a pneumatic cylinder using on-off valves. Experimental results show that the proposed algorithm for valve operation can be used to obtain fast and accurate position control and to prevent on-off valves from unnecessary switching.

• Journal of KIBIM
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• v.4 no.4
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• pp.13-23
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• 2014

After being introduced, Building Information Modeling (BIM) has been actively applied to the cost estimation of construction projects, and various studies on BIM based quantity take-off have been carried out. In practice, however, these calculations take considerable time, because BIM based quantity take-off is further conducted along with 2D-based quantity take-off. Studies on the quantity take-off using BIM spatial objects have been carried out on early stages of projects, but how this method differs from the existing quantity take-off method and how accurate it is in comparison have rarely been verified. Therefore, by comparing 2D based quantities with quantities through BIM spatial objects, this study analyzed the accuracy of quantity take-off using BIM spatial objects. To this end, the properties of BIM spatial objects and quantity calculable spatial types were analyzed, and existing 2D-based quantities and quantities extracted from BIM spatial objects were compared through a case study. As a result, the quantity of spatial objects found to be more by about 7.13% in 0.05% and therefore, this difference should be considered during quantity take-off using BIM spatial objects. Through the results of this study, we can improve the accuracy of quantity take-off using BIM spatial objects in the early stage of a construction project.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.7
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• pp.1170-1178
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• 2003

This paper provides approximate J estimates for off-centred, circumferential through-wall cracks in cylinders under bending and under combined tension and bending. The proposed method is based on the reference stress approach, where the dependence of elastic and plastic influence functions of J on the cylinder/crack geometry, the off-centred angle and strain hardening is minimised through the use of a proper normalising load. Based on published limited FE results for off-centred, circumferential through-wall cracks under bending, such normalising load is found, based on which the reference stress based J estimates are proposed for more general cases, such as for a different cylinder geometry and for combined loading. Comparison of the estimated J with extensive FE J results shows overall good agreements for different crack/cylinder geometries and for combined tension and bending, which provides sufficient confidence in the use of the proposed method to fracture mechanics analyses of off-centred circumferential cracks. Furthermore, the proposed method is simple to use, giving significant merits in practice.