• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.1
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• pp.49-55
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• 2005

This paper presents experiments on the evaluation of characteristics of ER fluids used for vibration control of application in intelligence type process control systems. Dynamic characteristics of the actuator(beam) embedded with the ER fluid can be controlled by changing the strength of the electric field applied on the ER fluids, thus provides a mean to avoid the resonance. In case electric field is supplied to the smart structure with ER fluids, vibration energy is dissipated more than the beam without electric field, because particles in ER fluid form a chain structure in the presence of electric field. The damping and stiffness of the beam with ER fluid are increased when the applied electric field increases. The characteristics of damping and stiffness of the ER fluid with various electric field strength were investigated by conducting a vibration test of the beam with ER fluid. If it applies characteristics of the ER fluids, it will be able to apply in the PLC control system for the vibration which occurs from process system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.1
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• pp.38-46
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• 2011

In this paper, we propose a calculation methodology of the service distance to assure the satisfactory quality of service for analogue and digital TV receivers. Using the field strength formulation for TV receiver based upon Rec. ITU-R P.1546, computational results are presented and discussed for both systems, and some important factors are reviewed in terms of the equivalent level of service, which must be kept due to ATV to DTV conversion. The presented method provides the predicted values of field strength at receiver areas to check whether transmission quality can be satisfied or not, and it can be also used for obtaining the protection ratio or separated distance from co-channel or adjacent interference signal.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.196-209
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• 2010

For the analysis of Acoustic Target Strength(TS) that indicates the scattered acoustic intensity from the underwater vehicles, an analysis program that is applicable to scatterers insonified by spherical wave source in near field is developed. In this program, the Physical Optics(PO) method is embedded as a base component. To increase the accuracy of the program, multiple bounce effects based on Geometrical Optics(GO) method are applied. To implement multiple bounce effects, GO method is used together with PO method. In detail, GO method has a concern in the evaluation of the effective area, and PO method is involved in the calculation of Acoustic Target Strength for the final effective area that is evaluated by GO method. For the embodiment of near field spherical wave source originated multiple bounce effects, image source concept is implemented additively to the existing multiple bounce algorithm which assumes plane wave insonification. Various types of models are tested to evaluate the reliability of the developed program and finally, a submarine is analyzed as an arbitrary scatterer.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.65-72
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• 2006

This study is about the estimation of the mechanical properties of cement grout material using a magnetic field treated water instead of tap water. The water that passed through a magnetic system is called MFTW. Similar research indicates that 5% of cement dosage can be saved by decreasing bleeding of concrete and improving resistance to freezing. The reason why MFTW can improve characteristics of concrete can be explained by molecular structure of water. Magnetic force makes water clusters into single molecule or small ones. Hence, the activity of water is improved by the magnetic force. While hydration of cement particles is on progress, the MFTW can penetrate the core region of cement particles more easily. Therefore, the hydration can be carried out more efficiently and the compression strength of concrete is highly improved. The sample of the sodium silicate cement grout's homogel using the MFTW results in highly compressive strength increases in compressive strength approximately from 20% to 50%.

• Journal of the Korea Institute of Construction Safety
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• v.6 no.1
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• pp.12-18
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• 2024

High-rise, large-scale, and diversification of buildings are possible, and the reduction of concrete cross-sections reduces the weight of the structure, thereby increasing or decreasing the height of the floor, securing a large number of floors at the same height, securing a large effective space, and reducing the amount of materials, rebar, and concrete used for designating the foundation floor. In terms of site construction and quality, a low water binder ratio can reduce the occurrence of dry shrinkage and minimize bleeding on the concrete surface. It has the advantage of securing self-fulfilling properties by improving fluidity by using high-performance sensitizers, making it easier to construct the site, and shortening the mold removal period by expressing early strength of concrete. In particular, with the rapid development of concrete-related construction technology in recent years, the application of ultra-high-strength concrete with a design standard strength of 100 MPa or higher is expanding in high-rise buildings. However, although high-rise buildings with more than 120 stories have recently been ordered or scheduled in Korea, the research results of developing ultra-high-strength concrete with more than 130 MPa class considering field applicability and testing and evaluating the actual applicability in the field are insufficient. In this study, in order to confirm the applicability of ultra-high-strength concrete in the field, a preliminary experiment for the member of a reduced simulation was conducted to find the optimal mixing ratio studied through various indoor basic experiments. After that, 130 MPa-class ultra-high-strength concrete was produced in a ready-mixed concrete factory in a mock member similar to the life size, and the flow characteristics, strength characteristics, and hydration heat of concrete were experimentally studied through on-site pump pressing.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.567-569
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• 1995

By using the ac field source which can change the applied field magnitude, frequency and dc offset field, the dynamic magnetoresistance characteristics of permalloy based multilayers which have different R-H(resistance-magnetic field) curves were monitored and compared with static magnetoresistance curves that were measured with electromagnet of VSM. Output of each sample according to the external field strength was identified and optimum bias position could be obtained.

• Geotechnical Engineering
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• v.3 no.2
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• pp.17-28
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• 1987

Reliability of the cone penetration test (CPT) for estimating shear strength of marine soils is investigated in this paper. For sands, the uncertainty about the angle of internal friction is analyzed. It includes the spatial variation of the soil and the model error in the equation used for interpretation. The most serious uncertainty encountered was the error in the interpretative models. Different methods of interpretation gave quite different values. Subjective opinion was introduced to combine all the interpretative models in a systematic manner. For clays, the undrained Shear Strength from the CPT results is usually =derived by empirical correlations between cone resistance and untrained shear strength from laboratory tests or field vane tests, expressed in terms of cone factor and function of overburden pressure. The uncertainty of the undrained shear strength is caused by data scatter of the cone factor in the correlation, model error of the cone factor, effect of anisotropy, and spatial variability of cone resistance. Among these uncertainties, the most serious one was the data scatter of the cone factor in the .correlation. Between the laboratory test and the field vane test used for correlation, the field vane test was more reliable.

• Journal of Industrial Technology
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• v.17
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• pp.137-143
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• 1997

The objective of this study is to find the strength properties of concrete using blast furnace slag. Its mechanical strength properties investigated include compressive strength, flexural strength, and tensile strength. The main expeirmental variables were cement type, coarse aggregate size(19, 25mm), and water/cement ratio(28, 32, 36%). The principal results obtained from this study are as follows ; it was possible to obtain the compressive strength of $500{\sim}700kg/cm^2$ concrete by using the blast furnace slag. Therefore, blast furnace slag was proved to be superior to ordinary portland cement in manufacturing the high strength concrete with the same mix conditions. In the near furture, concrete using blast furnace slag is expected to be practically used in the field.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.127-132
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• 1994

This study attemps to investigate the influence of heat of hydration occured during hardening on the strength development of high strength concrete. The concrete design strengths of 500kg/$\textrm{cm}^2$ and 700kg/$\textrm{cm}^2$ were considered to simulated the square columns having $80\times80cm$ and $100\times100cm$, respectively. Both standard curing and field curing specimen were prepared at the specified ages, and the cores were drilled out from the structure. The thermal sensors were installed into the specimen to measure the heat of hydration process occurred during the hardening. This paper tries to uncover the relationship between the temperature history of the concrete and strength development. The correlation of core strength and specimen strength with curing condition is also discussed. Further research is desired to enlight the relationship between strength and heat of hydration of high strength concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.8-13
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• 1995

High strength ready-miced concrete with delivering time of about 90 minutes is successfully produced at ready-mixed concrete plant and placed columns and retaining walls of a tall building without any problems. The design strength of the concrete is 450 kgf/$\textrm{cm}^2$ and the required average compressive strength is 540 kgf/$\textrm{cm}^2$ according to ACI 363R-84 report with assumed coefficient of variation of 12% For the producing of good quality concrete, many laboratary and field tests are carried out. As the results of this study, the slump loss of high strength concrete is largely influenced by kinds of superplasticizer. The measured pump pressure of high strength concrete with slump of 22cm is higher than that of normal strength concrete with slump of 18cm by about 20~30% The measured average 28-day compressive strength of the concrete is 551 kgf/$\textrm{cm}^2$ and the coefficient of variation is 2.3%