• Advanced Composite Materials
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• v.18 no.1
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• pp.77-93
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• 2009

This paper investigated the damage transition mechanism between the fiber-breaking mode and the fiber-avoiding crack mode when the fiber-length is reduced in the unidirectional discontinuous carbon fiber-reinforced-plastics (CFRP) composites. The critical fiber-length for the transition is a key parameter for the manufacturing of flexible and high-strength CFRP composites with thermoset resin, because below this limit, we cannot take full advantage of the superior strength properties of fibers. For this discussion, we presented a numerical model for the microscopic damage and fracture of unidirectional discontinuous fiber-reinforced plastics. The model addressed the microscopic damage generated in these composites; the matrix crack with continuum damage mechanics model and the fiber breakage with the Weibull model for fiber strengths. With this numerical model, the damage transition behavior was discussed when the fiber length was varied. The comparison revealed that the length of discontinuous fibers in composites influences the formation and growth of the cluster of fiber-end damage, which causes the damage mode transition. Since the composite strength is significantly reduced below the critical fiber-length for the transition to fiber-avoiding crack mode, we should understand the damage mode transition appropriately with the analysis on the cluster growth of fiber-end damage.

• Journal of Astronomy and Space Sciences
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• v.21 no.3
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• pp.201-208
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• 2004

In this paper we have examined the effect of dust charge density on nonlinear ion acoustic solitary wave which propagates obliquely with respect to the external magnetic field in a dusty plasma. For the dusty charge density below a critical value, the Sagdeev potential $\Psi1(n)$ has a singular point in the region n < 1, where n is the ion number density divided by its equilibrium number density. If there exists a dust charge density over the critical value, the Sagdeev potential becomes a finite function in the region n < 1, which means that there may exist the rarefactive ion acoustic solitary wave. By expanding the Sagdeev potential in the small amplitude limit up to on4 near n=1, we find the solution of ion acoustic solitary wave. Therefore we suggest that the dust charge density plays an important role in generating the rarefactive solitary wave.

• Research in Community and Public Health Nursing
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• v.13 no.1
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• pp.98-114
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• 2002

Purpose: This review examined literature relevant to adolescent's health behavior in order to identify key behaviors and factors related to health behaviors for targeting health promotion interventions. Method: A critical review of 29 research articles was carried out using the guidelines suggested by Cooper. Result: The majority of the studies were descriptive and cross-sectional. Generally. the study includes sub-dimensions such as general hygiene and daily life habit, safety and accident prevention, nutrition and eating (tobacco, drinking), exercise, mental health and stress management, health duty (drug, health examination, disease prevention). Factors highly related to health behaviors were age, living areas, economic status, parent health behaviors, parent health concern, social support, friends influence, self-efficacy, self-esteem, locus of control, and the perceived health status. Sex, parent education and health knowledge were not related to health behaviors of adolescents. Conclusion: Several conceptual and methodological problems were identified in the studies review, such as restricted conceptualization of health behaviors and sampling issues which limit the generalizability of the study outcomes. Further research is needed to enhance the concept clarification and generalizablity of the study results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.251-258
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• 2014

Sunroof tracks are manufactured by press-forming extruded aluminum sheets. During press forming, cracking occurs along the sharply bent edge. The final positions of the punch and die were measured on the section, and their relation to cracking was investigated. Finite element simulation of bending to the final position was done to find the critical strains. Three-point bending tests with different material orientations, hardnesses, bending edge lengths, and bending radii were carried out in the laboratory, and finite element simulation of the three-point bending tests was performed to find the critical strains.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.2
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• pp.115-122
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• 2008

Mostly used sensors have wired powering and two-way cable systems. It is difficult to employ wired sensor network in ubiquitous era because of a number of sensors and cables. Therefore, sensor networks move from wired systems to wireless systems for the future. However, the power source is a critical obstacle for wireless sensornodes. This research represents the new power source which supplies energy sensor node, maintains over 10 years, and thus replaces batteries with limit of lifetime. The system with piezo materials scavenges extra energies such as vibration and acceleration from the environment. Then it converts the scavenged mechanical energy to electrical energy for powering a sensor, a controller and a circuit for regulating voltage and transmitting sensor value. This study explains the properties of piezo material through theoretical analysis and experiments, and demonstrates powering sensor and transmitting data with stored energy (35mJ) for 14 sec. The developed system provides a solution to overcome the critical problem of making up wireless sensor networks.

• Ocean Systems Engineering
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• v.4 no.3
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• pp.215-241
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• 2014

Steel catenary riser (SCR) is a popular/economical solution for the oil/gas production in deep and ultra-deep water. The behavioral characteristics of SCR have a high correlation with the motion of floating production facility at its survival and operational environments. When large motions of surface floaters occur, such as FPSO in 100-yr storm case, they can cause unacceptable negative tension on SCR near TDZ (touch down zone) and the corresponding elastic deflection can be large due to local dynamic buckling. The generation, propagation, and decay of the elastic wave are also affected by SCR and seabed soil interaction effects. The temporary local dynamic buckling vanishes with the recovery of tension on SCR with the upheaval motion of surface floater. Unlike larger-scale, an-order-of-magnitude longer period global buckling driven by heat and pressure variations in subsea pipelines, the sub-critical local dynamic buckling of SCR is motion-driven and short cycled, which, however, can lead to permanent structural damage when the resulting stress is greatly amplified beyond the elastic limit. The phenomenon is extensively investigated in this paper by using the vessel-mooring-riser coupled dynamic analysis program. It is found that the moment of large downward heave motion at the farthest-horizontal-offset position is the most dangerous for the local dynamic buckling.

• Steel and Composite Structures
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• v.8 no.6
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• pp.457-473
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• 2008

Yielding of the internal steel reinforcement is an important mechanism that influences the Intermediate Crack-induced debonding (IC debonding) behavior in FRP-strengthened RC members since the FRP is required to carry additional forces beyond the condition of steel yielding. However, rational design practice dictates an appropriate limit state is defined when steel yielding is assured prior to FRP debonding. This paper proposes a criterion which correlates the occurrence of IC debonding to the formulation of a critical steel yielding length. Once this length is exceeded the average bond stress in the FRP/concrete interface exceeds its threshold value, which proves to correlate with the average bond resistance in an FRP/concrete joint under simple shear loading. This proposed IC debonding concept is based on traditional sections analysis which is conventionally applied in design practice. Hence complex bond stress-slip analyses are avoided. Furthermore, the proposed model incorporates not only the bond properties of FRP/concrete interface but also the beam geometry, and properties of steel and FRP reinforcement in the analysis of IC debonding strength. Based upon a solid database, the validity of the proposed simple IC debonding criterion is demonstrated.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1244-1250
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• 2009

In this study it is intended to review the moving characteristics of smoke by performing visualization for the calculation of the optimal smoke exhaust air volume in case a fire occurs in tunnels where transverse ventilation is applied, and to obtain basic data necessary for the design of smoke exhaust systems by deriving optimal smoke exhaust operational conditions under various conditions. As a result of this study, when the critical velocity in the tunnel is 1.75 m/s and 2.5 m/s, the optimal smoke exhaust air volume has to be more than $173\;m^3/s$, $236\;m^3/s$ for the distance of the smoke moving which can limit the distance to 250m. In addition, in case of uniform exhaust the generated smoke is effectively taken away if the two exhaust holes near the fire region are opened at the same time.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.543-550
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• 2016

The Active Superconducting Current Controller (ASCC) is a new type of Superconducting Fault Current Limiters (SFCL) which can limit the fault current in different modes. It also has the particular abilities of compensating active and reactive powers for electrical networks. In this paper, it is confirmed that the performance of ASCC in different operating modes introduces a limiting impedance in series with the network which can even degrade the transient stability and the operation of the Over-Current Relays (OCR) employed in a power system. In addition, the model of a three-phase ASCC is simulated, and the effect of descriptive modes on the current limiting level is investigated. For the transient stability analysis, a single machine-infinite bus system is tested, and the effect of operation modes is studied based on an equal area criterion obtaining the critical time and the critical angle. Modifying the setting parameters of OCR such as time dial and pick-up current, the protective coordination is also studied in different operating modes.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2210-2211
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• 2008

In this paper, we investigated the quenching characteristics of a superconducting fault current limiter (SFCL) with connection of $2{\times}3$ matrixes. This SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit the fault current. When the fault occurs, the magnetic field generated in the reactor connected in parallel was applied to the two superconducting units of the current-limiting part to reduce of inhomogeneous critical current behavior between the superconducting units. The quenching behavior of a superconducting unit in the trigger part was affected by the increase of turn numbers. This is because of the difference of current distribution between the inductance of the reactors and the resistance generated in the superconducting units in trigger part. We confirmed that the voltage differences between two superconducting units of the current-limiting part were decreased. This is because of the improvement of inhomogeneous critical current behavior between the superconducting units according to the increase of external magnetic field.