• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.5
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• pp.933-940
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• 2010

A numerical analysis for the space frame structure under ballistic and blast loads was performed using LS-DYNA, a commercial code. The space frame structure was developed to be adapted to the ground vehicle in the future and it was designed to build with Al7039 frames and lightweight multi-layered panels for the purpose of weight reduction and shock mitigation. The analyses have done for side impacts by a cylindrical projectile and Comp. C-4 explosive representing major threats to the vehicle. The deformed shape of the panel section and stresses as well as accelerations of the frames calculated from LS-DYNA were compared to the test results to validate the analysis model. The internal energies for panels and frames from LS-DYNA were also compared to each other to discern their role in absorbing the ballistic and blast impact.

• Journal of Power Electronics
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• v.17 no.3
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• pp.744-755
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• 2017

With the high penetration of various sustainable energy sources, the control and protection of Microgrids has become a challenging problem considering the inherent current limitation feature of inverter-based Distributed Generators (DGs) and the bidirectional power flow in Microgrids. In this paper, a hybrid control and protection scheme is proposed, which combines the traditional inverse-time overcurrent protection with the biased differential protection for different feeders with different kinds of loads. It naturally accommodates various control strategies such as P-Q control and V-f control. The parameter settings of the protection scheme are analyzed and calculated through a fast Fourier transform algorithm, and the stability of the control strategy is discussed by building a small signal model in MATLAB. Different operation modes such as the grid-connected mode, the islanding mode, and the transitions between these two modes are ensured. A Microgrid model is established in PSCAD and the analysis results show that a Microgrid system can be effectively protected against different faults such as the single phase to ground and the three phase faults in both the grid-connected and islanded operation modes.

• Transactions on Electrical and Electronic Materials
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• v.18 no.4
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• pp.190-194
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• 2017

Present-day solar panels incorporate inverters as their core components. Switching devices driven by specialized power controllers are operated in a transformerless inverter topology. However, some challenges associated with this configuration include the absence of isolation, causing leakage currents to flow through various components toward ground. This inevitably causes power losses, often being also the primary reason for the power inverters' analog equipment failure. In this paper, various aspects of the leakage currents are studied using different circuit analysis methods. The primary objective is to convert the leakage current energy into a usable DC voltage source. The research is focused on harvesting the leakage currents for producing circa 1.1 V, derived from recently developed rectifier circuits, and driving a $200{\Omega}$ load with a power in the milliwatt range. Even though the output voltage level is low, the harvested power could be used for charging small batteries or capacitors, even driving light loads.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.424-431
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• 2006

Many types of tuned mass dampers (TMDs), such as active TMDs, multiple TMDs, hybrid TMDs etc., have been studied to effectively reduce the dynamic responses of a structure subjected to various types of dynamic loads. In this study, we replace a passive damper by a semi-active tuned mass damper to improve the control performance of conventional TMDs (STMD). An idealized variable damping device is used as semi-active dampers. These semi-active dampers can change the properties of TMDs in real time based on the dynamic responses of a structure. The control performance of STMD is investigated with respect to various types of excitation by numerical simulation. Groundhook control algorithm is used to appropriately modulate the damping force of semi-active dampers. The control effectiveness between STMD and a conventional passive TMD, both under harmonic and random excitations, is evaluated and compared for a single-degree-of-freedom (SDOF) structure. Excitations are applied to the structure as a dynamic force and ground motion, respectively. The numerical studies showed that the control effectiveness of STMD is significantly superior to that of the passive TMD, regardless of the type of excitations.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.105-112
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• 2006

Liquefaction-induced lateral spreading has been the most extensive damage to pile foundations during earthquakes. However, a case of pile failure was reported despite the fact that a large margin of safety factor was employed in their design. This means that the current seismic design method of pile is not agreeable with the actual failure mechanism of pile. Newly proposed failure mechanism of pile is a pile failure based on buckling instability. In this study, failure behavior of pile embedded in liquefied soil deposits was analyzed considering lateral spreading and buckling instability performing 1g shaking table test. As a result, it can be concluded that the pile subjected to excessive axial loads ($near\;P_{cr}$) can fail by buckling instability during liquefaction. When lateral spreading took place in sloping grounds, lateral spreading increased lateral deflection of pile and reduced the buckling load, promoting more rapid collapse. In addition, buckling shape of pile was observed. In the ease of pile buckling, hinge formed at the middle of the pile, not at the bottom. And in sloping grounds, location of hinge got loiter compared with level ground because of the effects of lateral spreading.

• Steel and Composite Structures
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• v.35 no.2
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• pp.279-294
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• 2020

Foundation of a building is damaged under service loads during construction. First visit shows that the foundation has been punched at the 6 column's foot region led to building rotation. Foundation shear punching occurring has made some stresses and deflections in construction. In this study, progressing of damage caused by foundation shear punching and inverse loading in order to resolve the building rotation has been evaluated in the foundation and frame of building by finite element modeling in ABAQUS software. The stress values of bars in punched regions of foundation has been deeply exceeded from steel yielding strength and experienced large displacement based on software's results. On the other hand, the values of created stresses in the frame are not too big to make serious damage. In the beams and columns of ground floor, some partial cracks has been occurred and in other floors, the values of stresses are in the elastic zone of materials. Finally, by inverse loading to the frame, the horizontal displacement of floors has been resolved and the values of stresses in frame has been significantly reduced.

• Structural Engineering and Mechanics
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• v.10 no.6
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• pp.517-532
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• 2000

A direct output feedback control scheme was recently proposed by the authors for single-story building structures resting on flexible soil body. In this paper, the control scheme is extended to mitigate the seismic responses of multi-story buildings. Soil-structure interaction is taken into account in two parts: input at the soil-structure interface/foundation and control algorithm. The former reflects the effect on ground motions and is monitored in real time with accelerometers at foundation. The latter includes the effect on the dynamic characteristics of structures, which is formulated by modifying the classical linear quadratic regulator based on the fundamental mode shape of the soil-structure system. Numerical result on the study of a $\frac{1}{4}$-scale three-story structure, supported by a viscoelastic half-space of soil mass, have demonstrated that the proposed algorithm is robust and very effective in suppressing the earthquake-induced vibration in building structures even supported on a flexible soil mass. Parametric studies are performed to understand how soil damping and flexibility affect the effectiveness of active tendon control. The selection of weighting matrix and effect of soil property uncertainty are investigated in detail for practical applications.

• Structural Engineering and Mechanics
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• v.20 no.1
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• pp.1-20
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• 2005

The present paper deals with the seismic response analysis and the evaluation of most likely failure modes for a water storage structure. For the stress analysis, a 3-D mathematical model has been adopted to represent the structure appropriately. The structure has been analyzed for both static and seismic loads. Seismic analysis has been carried out considering the hydrodynamic effects of the contained water. Based on the stress analyses results, the most likely failure modes viz. tensile cracking and compressive crushing of concrete for the various structural elements; caused by the seismic event have been investigated. Further an attempt has also been made to quantify the initial leakage rate and average emptying time for the structure during seismic event after evaluating the various crack parameters viz. crack-width and crack-spacing at the locations of interest. The results are presented with reference to peak ground acceleration (PGA) of the seismic event. It has been observed that, an increase in PGA would result in significant increase in stresses and crack width in the various structural members. Significant increase in initial leakage rate and decrease in average emptying time for the structure has also been observed with the increase in PGA.

• Earthquakes and Structures
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• v.8 no.1
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• pp.19-35
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• 2015

This study compares the seismic performances of two reinforced concrete frame specimens tested by the pseudo-dynamic procedure. The pair of 3-storey, 3-bay frames specimens are constructed with typical characteristics of older construction which is lacking seismic design. One of the specimens is a bare frame while the other is infilled with low-strength autoclave aerated concrete (AAC) block masonry. The focus of this study is to investigate the influence of low strength masonry infill walls on the seismic response of older RC frames designed for gravity loads. It is found that the presence of weak infill walls considerably reduce deformations and damage in the upper stories while their influence at the critical ground story is not all that positive. Infill walls tend to localize damage at the critical story due to a peculiar frame-infill interaction, and impose larger internal force and deformation demands on the columns and beams bounding the infills. Therefore the general belief in earthquake engineering that infills develop a second line of defence against lateral forces in seismically deficient frames is nullified in case of low-strength infill walls in the presented experimental research.

• Journal of the Korean Solar Energy Society
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• v.34 no.3
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• pp.75-81
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• 2014

Recently, the use of renewable energy has been attracted due to the interest in energy-saving and the reduction of CO2 emission. In order to reduce the energy consumption of the cooling and the heating in the field of the architectural engineering, heat pump systems using renewable energy have been developed and used in various applications. In many researches, integrated heat pump systems are suggested which use solar and geothermal heat as the heat source for cooling and heating. However, it is still difficult to predict the performance of the systems, because the characteristic of heat exchange in each system is complicated and various. In this system, the performance prediction simulation of the heat pump was developed using a dynamic simulation model. This paper describes the summary of the suggested systems and the result of the simulation. The average temperature of the heat source, heating loads and COP were calculated with the cases of different local conditions, different system composition and different operation time by TRNSYS 17.