• Journal of the Korean Society of Industry Convergence
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• v.23 no.5
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• pp.747-756
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• 2020

In recent years, measurement in a smart-phone environment is attracting attention in various fields due to its easy set-up process, various functions, convenience and expandability. Even in the field of safety evaluation and maintenance of large-scale infra-structures, the appropriate application of these effective and convenient measurement techniques can be of great help. In this paper, an experimental study was conducted to investigate the effectiveness, problems and complementary methods of applying smart-phone accelerometers to the measurement in infra-structure such as bridges. In model bridge subjected to impact and moving loads, the measured accelerations using a smart-phone and a professional accelerometer were directly compared in time domain. And the statistical and frequency characteristics of the measured signal and transfer function were also examined in frequency domain. The results show that the accuracy of measurement using smart-phone sensor is primarily affected by its incomplete sampling performance. In conclusion, smart-phone sensors cannot be considered suitable for precise assessment, where measurements must be accurate over a wide frequency range, but we can say that the technique is still useful and fairly accurate for some purpose over a limited frequency range, such as the low pass frequency range, which is a major concern for civil structures.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.170-176
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• 1987

This study is concerned with dynamic characteristics of a circular ring with a concentrated mass attached. The equations of motion are set up and are solved by using Laplace transformation. The ratio of a concentrated mass to the mass of circular ring is used as a parameter. Experiment was performed by employing impulse test and the results show good agreement with those of analysis. The results of this study can be utilized in vibrational analysis of axisymmetric shells with slight asymmetries.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.2
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• pp.53-58
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• 2017

This study introduces the case of pipelines installed in subsea conditions and buried offshore. Such installations generate pore water pressure under the seabed because of cyclic wave excitation, which is an environmental load, and consistent cyclic wave loading that reduce the soil shear strength of the seabed, possibly leading to liquefaction. Therefore, in view of the liquefaction of the seabed, stability of the subsea pipelines should be examined via calculations using a simple method for buried subsea pipelines and floating structures. Particularly, for studying the possible liquefaction of the seabed in regard to subsea pipelines, high waves of a 10- and 100-year period and the number of occurrences that are affected by the environment within a division cycle of 90 s should be applied. However, when applying significant wave heights (HS), the number of occurrences within a division cycle of 3 h are required to be considered. Furthermore, to research whether dynamic vertical load affect the seabed, mostly a linear wave is used; this is particularly necessary to apply for considering the liquefaction of the seabed in the case of pile structure or subsea pipeline installation.

• Journal of Power Electronics
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• v.4 no.3
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• pp.161-168
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• 2004

This paper presents a new circuit topology of high-frequency soft switching commutation boost type PWM chopper-fed DC-DC power converter with a loadside auxiliary passive resonant snubber. In the proposed boost type chopper-fed DC-DC power converter circuit operating under a principle of ZCS turn-on and ZVS turn-off commutation, the capacitor and inductor in the auxiliary passive resonant circuit works as the lossless resonant snubber. In addition to this, the voltage and current peak stresses of the power semiconductor devices as well as their di/dt or dv/dt dynamic stress can be effectively reduced by the single passive resonant snubber treated here. Moreover, it is proved that chopper-fed DC-DC power converter circuit topology with an auxiliary passive resonant snubber could solve some problems on the conventional boost type hard switching PWM chopper-fed DC-DC power converter. The simulation results of this converter are illustrated and discussed as compared with the experimental ones. The feasible effectiveness of this soft witching DC-DC power converter with a single passive resonant snubber is verified by the 5kW, 20kHz experimental breadboard set up to be built and tested for new energy utilization such as solar photovoltaic generators and fuel sell generators.

• Journal of the Korean Operations Research and Management Science Society
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• v.23 no.2
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• pp.187-200
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• 1998

This paper presents an original approach for solving short-term power scheduling in extended power system with two fuels in a unit and a limited fuel using Lagrangian relaxations. The underlying model incorporates the full set of costs and constraints including setup, production, ramping, and operational status, and takes the form of a mixed integer nonlinear control problem. Moreover, the mathematical model developed includes two fuels in a unit and a limited fuel, regulation reserve requirements of prespecified group of units. Lagrangian relaxation is used to disaggregate the model by generator into separate subproblems which are then solved with a nested dynamic program including empirical knowledges. The strength of the methodology lies partially in its ability to construct good feasible solutions from information provided by the dual. Thus, the need for branch-and-bound is eliminated. In addition, the inclusion of two fuels in a unit and a limited fuel provides new insight into the limitations of current techniques. Computational experience with the proposed algorithm indicates that Problems containing up to 23 units including 8 unit used two fuels and 24 time periods can be readily solved in reasonable times. Duality gaps of less than 4％ were achieved.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.232-237
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• 2007

The deformation of polymers under high loading-rate conditions will be a governing factor to be considered in their impact-resistant applications such as protective shields and transparent armor. In this paper, the deformation and fracture behaviors of polymeric materials such as PE, PC and PEEK have been investigated by Taylor Impact tests. Taylor cylinder impact tests and high speed photography are introduced to examine the deformation behavior under dynamic loading condition. 20 mm air gun was used to perform the impact experiments. Cylindrical projectiles have been impacted onto a hardened steel anvil at a velocity ranging from 100 to $350\;ms^{-1}.$ Along the barrel line, a photo-sensor which measures the speed of the projectile, four digital cameras which has shutter speed of 1/917,000sec and a rigid anvil were set up. After impact experiments, the shapes of projectiles and images taken using high speed cameras were analysed. Depending on materials adopted, they showed a variety in deformation and fracture behaviors.

• Structural Engineering and Mechanics
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• v.46 no.1
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• pp.75-90
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• 2013

In order to identify damage of highway bridges rapidly, a method for damage identification using dynamic response of bridge induced by moving vehicle and static test data is proposed. To locate damage of the structure, displacement energy damage index defined from the energy of the displacement response time history is adopted as the indicator. The displacement response time histories of bridge structure are obtained from simulation of vehicle-bridge coupled vibration analysis. The vehicle model is considered as a four-degree-of-freedom system, and the vibration equations of the vehicle model are deduced based on the D'Alembert principle. Finite element method is used to discretize bridge and finite element model is set up. According to the condition of displacement and force compatibility between vehicle and bridge, the vibration equations of the vehicle and bridge models are coupled. A Newmark-${\beta}$ algorithm based professional procedure VBAP is developed in MATLAB, and used to analyze the vehicle-bridge system coupled vibration. After damage is located by employing the displacement energy damage index, the damage extent is estimated through the least-square-method based model updating using static test data. At last, taking one simply supported bridge as an illustrative example, some damage scenarios are identified using the proposed damage identification methodology. The results indicate that the proposed method is efficient for damage localization and damage extent estimation.

• Geomechanics and Engineering
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• v.15 no.2
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• pp.775-781
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• 2018

Shake table tests were conducted on scaled tunnel model to investigate the mechanism and effect of seismic loadings on horseshoe scaled tunnel model in ground fissure site. Key technical details of the experimental test were set up, including similarity relations, boundary conditions, sensor layout, modelling methods were presented. Synthetic waves and El Centro waves were adopted as the input earthquake waves. Results measured from hanging wall and foot wall were compared and analyzed. It is found that the seismic loadings increased the subsidence of hanging wall and lead to the appearance and propagation of cracks. The values of acceleration, earth pressure and strain were greater in the hanging wall than those in the foot wall. The tunnel exhibited the greatest earth pressure on right and left arches, however, the earth pressure on the crown of arch is the second largest and the inverted arch has the least earth pressure in the same tunnel section. Therefore, the effect of the hanging wall on the seismic performance of metro tunnel in earth fissure ground should be considered in the seismic design.

• Journal of the Korean Institute of Landscape Architecture
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• v.33 no.5 s.112
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• pp.114-122
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• 2005

Anyang city performed a design competition for the existing paper mill site and this design is the work that was submitted to that competition. The design instructions for the competition were about an organic site which had harmony of aboveground park and underground parking lot, establishment of park planning which is fit for the features of nearby areas, and security of proper parking space. This design criteria set the design concept to a new wave of Anyang by reflecting the design instructions of prize contest and features of the site and developed it as three waves. First, the eco wave, one of three waves, means that it compose the ecological healthy park and urban environment together with restoration and preservation of Suamcheon (stream), and futhermore the waves that the natural resource are maintained in a delicate ecological balance as the water resource of Anyang city are connected to the axis of mountain resource. Secondly, the emotion wave indicates that the wave toward culture and art emotional park that stimulates and fills up the emotion to makes impoverishing modems minds fertile. Thirdly, the health wave means the waves toward a park to keep the sound of minds and bodies of Anyang citizens, and healthy and sound life as well as the waves toward a park to contribute the healthy leap and development of Anyang. These three waves will enrich the park keeping the dynamic relationship mutually and will be a new culture and art code of Anyang city.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.104-109
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• 2009

In order to apply FBG(Fiber Bragg Grating) sensor as one of reliable sensors in the commercial railway structure, the reliability of FBG sensor in the mechanical strength viewpoint have to be confirmed and the maximum strain should surpass the fracture strain of the host structure to measure the measurands until the host structures fail. In this paper, several factors that influence the mechanical failure strength of fiber Bragg grating sensors were analyzed. A set-up for dynamic tensile testing of optical glass fibers with fiber Bragg gratings was made. To increase the FBG failure strength, techniques relying on the H2 loading treatment and stripping methods were established and testified as a result of the tensile strength test of optical fibers.