• Structural Engineering and Mechanics
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• v.21 no.2
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• pp.185-204
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• 2005

Variations in system parameters due to uncertainties may result in system performance deterioration. Uncertainties in modeling of structures are often considered to ensure that control system is robust with respect to response errors. Hence, the uncertain concept plays an important role in vibration control of the engineering structures. The paper discusses the robustness of the stability of vibration control systems with uncertain parameters. The vibration control problem of an uncertain system is approximated by a deterministic one. The uncertain parameters are described by interval variables. The uncertain state matrix is constructed directly using system physical parameters and avoided to use bounds in Euclidean norm. The feedback gain matrix is determined based on the deterministic systems, and then it is applied to the actual uncertain systems. A method to calculate the upper and lower bounds of eigenvalues of the close-loop system with uncertain parameters is presented. The lower bounds of eigenvalues can be used to estimate the robustness of the stability the controlled system with uncertain parameters. Two numerical examples are given to illustrate the applications of the present approach.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.881-892
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• 2017

Design and management of concrete slabs in concrete-faced rock-fill dams are crucial issues for stability and overall dam safety since cracks in the concrete face induced by stress, shrinkage, and deterioration can cause severe leakage from the reservoir into the dam. Especially, the increase of dam height to a certain level to enhance the storage capacity and to improve hydraulic stability can lead to undesirable deformation behavior and stress distribution in the existing dam body and in the concrete slabs. In such conditions, simulation of a concrete slab with a numerical method should involve the use of an interface element because the behavior of the concrete slab does not follow the behavior of the dam body when the dam body settles due to the increase of dam height. However, the interfacial properties between the dam body and the concrete slab have yet to be clearly defined. In this study, construction sequence of a 125 m high CFRD in South Korea is simulated with commercial FDM software. The proper interfacial properties of the concrete slab are estimated based on a comparison to monitored vertical displacement history obtained from the concrete slab. Possibility of shear strength failure under the critical condition is investigated based on the simplified model. Results present the significance of the interfacial properties of the concrete slab.

• Journal of Mechanical Science and Technology
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• v.15 no.10
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• pp.1442-1450
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• 2001

The EGR system has been widely used to reduce nitrogen oxides (NO$\_$x/) emission, to improve fuel economy and suppress knock by using the characteristics of charge dilution. However, as the EGR rate at a given engine operating condition increases, the combustion instability increases. The combustion instability increases cyclic variations resulting in the deterioration of engine performance and emissions. Therefore, the optimum EGR rate should be carefully determined in order to obtain the better engine performance and emissions. An experimental study has been performed to investigate the effects of EGR on combustion stability, engine performance,70x and the other exhaust emissions from 1.5 liter gasoline engine. Operating conditions are selected from the test result of the high speed and high acceleration region of SFTP mode which generates more NO$\_$x/ and needs higher engine speed compared to FTP-75 (Federal Test Procedure) mode. Engine power, fuel consumption and exhaust emissions are measured with various EGR rate. Combustion stability is analyzed by examining the variation of indicated mean effective pressure (COV$\_$imep/) and the timings of maximum pressure (P$\_$max/) location using pressure sensor. Engine performance is analyzed by investigating engine power and maximum cylinder pressure and brake specific fuel consumption (BSFC)

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1715-1720
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• 2007

The CSC-based HVDC system links the Jeju system to the mainland system. Because CSC-based HVDC is installed in Jeju, the reactive power is needed to transfer active power through the HVDC. In order to supply reactive power, switched capacitors and synchronous condensers are installed in Jeju system. The deterioration of established synchronous condensers, however, causes a reactive power supply capability decline and high maintenance cost. It brings about the instability of Jeju system and the incremental of maintenance and repair costs. In the future the installation of wind generators and additional HVDC system would aggravate the stability of Jeju system. Therefore, it needs to consider a countermeasure against above problems. In this paper, Analysis of several contingencies of Jeju system was peformed, and some contingencies caused voltage-reactive power problem was known. CPF method was introduced in order to make countermeasures to replace the synchronous condensers and to solve the voltage-reactive power problem. The location and capacity of reactive power sources were also decided. It could guarantee medium and long term stability of Jeju system.

• 보존과학연구
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• s.27
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• pp.103-128
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• 2006

Rock properties of the five storied stone pagoda in the Mooryangsa temple are consist mainly in medium grained biotite granite with partly pegmatite veinlet. A part of the foundation stone is substituted in identical rock properties of the pagoda. The upper part of the pagoda is used purples and stone, gray shale and granodiorite. The most serious problem of the pagoda is structual instability from centered subsidence of the ground in northwestern direction remarkably. In southern view, the upper part of the pagoda also is slanted a little in right, it will need reinforcement by engineering method for structual stability of the stone pagoda. Weathering states of the stone pagoda are affected results of natural and artifical factors due to the surface-exfoliation, fine-fissure, crack, falling offs. On the rock surface of the pagoda, ferro-manganese hydroxide compounds are coated along the rainpathway. Also, bryophyte range concentration spreads raindrops face of roof rock properties, which areadd biological weathering effects. For the synthetic evaluation of the deterioration state, we make detailed surface weathering maps, it will be contribute to investigation for future conservation schemes.

• Ecology and Resilient Infrastructure
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• v.5 no.2
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• pp.82-87
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• 2018

Proliferation of algae on the surface of concrete or mortar in aquatic habitat has a negative impact on maintenance of concrete-based structures. Growth of algae may decrease stability of structure by bio-deterioration. In this study, we developed a functional mortar for restraining bio-deterioration by using $Cu^{2+}$ ion. The mortar contains soluble glass beads made of $Cu^{2+}$ ion, which can dissolve into water slowly. Mortars prepared with different ratio of glass beads (0, 2, 5, 10, and 15%) were placed in a culture medium with algae and incubated over a month period. Water chemistry, chlorophyll-a, and extracellular enzyme activities were measured. The incubation was conducted in both freshwater and seawater conditions, to assess applicability to both aquatic conditions. Overall, mortar with Cu glass exhibited lower chlorophyll-a content, suggesting that the functional mortar reduced algal growth. DOC concentration increased because debris of dead algae increased. Cu glass also decreased phosphatase activity, which is involved in the regeneration of inorganic P from organic moieties. Since, P is often a limiting nutrient for algal production, algal growth may be inhibited. Activities of ${\beta}$-glucosidase and N-acetylglucosaminidase were not significantly affected because carbon and nitrogen mineralization may not be influenced by the Cu glass beads. Our study suggests that functional mortar with Cu glass beads may reduce the growth of algae on the surface, while it has little environmental impact.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1450-1458
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• 2018

Commutation failures can deteriorate the availability of high-voltage direct current (HVDC) links and may lead to outage of the HVDC system. Most commutation failures are caused by voltage reduction due to ac system faults on inverter side. The commutation failure process can be divided into two stages. The first stage, from the occurrence to the clearing of faults, is called 'Deterioration Stage'. The second stage, from the faults clearing to restoring the power system stability, is called 'Recovery Stage'. Based on the analysis of the commutation failure process, this paper proposes a direct-current fuzzy controller including prevention and recovery controller. The prevention controller reduces the direct current to prevent Commutation failures in the 'Deterioration Stage' according to the variation of ac voltage. The recovery controller magnifies the direct current to speed up the recovery of power system in the 'Recovery Stage', based on the recovery of direct voltage. The validity of this proposed fuzzy controller is further proved by simulation with CIGRE HVDC benchmark model in PSCAD/EMTDC. The results show the commutation failures can be mitigated by the proposed direct-current fuzzy controller.

• Food Science and Preservation
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• v.4 no.2
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• pp.189-196
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• 1997

Blanching conditions for immatured soybeans were optimized by analyzing the effects of various time/temperature blanch treatment on the activities of peroxidase and lipoxygenase, the stability of vitamin C and color, and moisture content in immatured soybeans for the purpose of minimizing quality deterioration during frozen storage. Blanching at 96$^{\circ}C$ for 70 sec led to maximum inactivation of lipoxygenase in the immatured soybeans, while my blanching conditions tested in this study were not enough to inactivate peroxidase. Blanching at 82$^{\circ}C$ for 60 sec resulted in the highest amount of vitamin C remaining in the immatured soybeans after blanching. Hunter -a/b ratios of immatured soybeans blanched at 82$^{\circ}C$ for 60 sec and hue values (ΔE) of the immatured soybeans blanched at 76$^{\circ}C$ for 60 sec showed the closest values to those of fresh products. The changes in moisture content of immatures soybeans was not so significant after blanching. In conclusion, it was suggested that immatured soybeans be blanched at 96$^{\circ}C$ for 70 sec to minimize lipoxygenase activity and resulting quality deterioration, while blanching at 82$^{\circ}C$ for 60 sec was recommended to stabilize vitamin C and color.

• Tunnel and Underground Space
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• v.26 no.6
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• pp.484-492
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• 2016

This study is the numerical analysis for the ground stability assessment in ${\bigcirc}{\bigcirc}$mine. The subsidence factors applied to the numerical analysis were as follows. First, the deterioration of the rock mass properties by excavation of the disturbed zone. Second, using the average lateral pressure coefficient of Korea. Third, a study of the mine history. Fourth, the excavating collapsed rock mass in numerical analysis based on the assumption that the rock mass around the goaf was collapsed due to the mining. The developed methods were applied to the cross section (5+10) of the actual subsidence in ${\bigcirc}{\bigcirc}$mine. The feasibility of the numerical analysis methods was confirmed by providing the same results as those of the actual subsidence. Next, the developed methods were applied to the cross section (3+10) that had a high probability of subsidence and the ground stability was evaluated. The analysis results show that the vertical displacement for the 5+10 cross section occurs at a maximum of 46 mm, whereas the analysis results show that the vertical displacement for the 3+10 cross section occurs at a maximum of 7 mm. Hence, it is concluded that the probability for subsidence is low.

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.3
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• pp.424-431
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• 2017

Objective: Study on the application of high pressure processing (HPP) for dark-firm-dry (DFD) beef was conducted to observe whether HPP has any impact on physical properties and to evaluate oxidative deterioration during refrigerated storage under vacuum. Methods: The longissimus lumborum muscles obtained from Friesian Holstein steers ($33{\pm}0.5$ months old) with 24-h postmortem pH higher than 6.0 were vacuum-packed and subjected to pressurization at 200, 400, and 600 MPa for 180 s at $15^{\circ}C{\pm}2^{\circ}C$; the samples were then stored for 9 days at $4^{\circ}C{\pm}1^{\circ}C$ and compared with control (0.1 MPa). Results: HPP increased meat pH by 0.1 to 0.2 units and the tenderness of cooked DFD beef significantly with no significant effects on meat texture profile. The stability of meat pH was well maintained during refrigerated storage under vacuum. No clear effects were found on the activity of catalase and superoxide dismutase, however, glutathione peroxidase activity was significantly reduced by high pressure. HPP and storage time resulted in aroma changes and the increasing amount of malondialdehyde and metmyoglobin relative composition. Conclusion: Although the increasing amount of malondialdehyde content, metmyoglobin formation and aroma changes in HPP-treated samples could not be avoided, HPP at 200 MPa increased $L^*$ and $a^*$ values with less discoloration and oxidative deterioration during storage.