• Wind and Structures
• /
• v.11 no.3
• /
• pp.193-208
• /
• 2008

This paper focuses on assessing the failure of one of the transmission towers that collapsed in Winnipeg, Canada, as a result of a microburst event. The study is conducted using a fluid-structure numerical model that was developed in-house. A major challenge in microburst-related problems is that the forces acting on a structure vary with the microburst parameters including the descending jet velocity, the diameter of the event and the relative location between the structure and the jet. The numerical model, which combines wind field data for microbursts together with a non-linear finite element formulation, is capable of predicting the progressive failure of a tower that initiates after one of its member reaches its capacity. The model is employed first to determine the microburst parameters that are likely to initiate failure of a number of critical members of the tower. Progressive failure analysis of the tower is then conducted by applying the loads associated with those critical configurations. The analysis predicts a collapse of the conductors cross-arm under a microburst reference velocity that is almost equal to the corresponding value for normal wind load that was used in the design of the structure. A similarity between the predicted modes of failure and the post event field observations was shown.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.11 no.2
• /
• pp.23-31
• /
• 2008

The configuration model of a ballute type RAID(Ram Air Inflated Decelerator) for reducing the high speed and high revolution of smart submuntion is designed and tested. Three dimensional incompressible turbulent flow computational fluid dynamic analysis for the assembly of ballute and submunition is performed and pressure distribution, velocity, and drag around the assembly is calculated. Aerodynamic characteristics of the ballute assembly such as air flow inside and outside of the ballute and pressure distribution is clearly shown and it's drag coefficient is computed. Trajectory analysis of the submunition is performed and is in good agreement with the descending trajectory data of experimental model tested.

• Journal of information and communication convergence engineering
• /
• v.12 no.2
• /
• pp.75-82
• /
• 2014

Dispersion management (DM), optical phase conjugation (OPC), and the combination of DM and OPC are promising techniques to compensate for optical signal distortion due to group velocity dispersion and nonlinear Kerr effects. The system performance improvement in DM links combined with OPC has been reported; however, the fixed residual dispersion per span (RDPS) usually used in these links restricts the flexibility of link configuration. Thus, in this paper, a flexible optical link configuration with artificially distributed single-mode fiber (SMF) lengths and RDPS in the combination of DM and OPC is proposed. Simulation results show that the best artificial distribution pattern is the gradually descending distribution of SMF lengths and the gradually ascending distribution of RDPS, as the number of fiber spans is increased, regardless of the average RDPS, the optimal net residual dispersion, and the dispersion coefficient of the dispersion compensating fiber.

• Journal of information and communication convergence engineering
• /
• v.15 no.4
• /
• pp.205-211
• /
• 2017

Combining dispersion-managed optical links with midway optical phase conjugation (OPC) is a possible method of compensating for optical signal distortion due to group velocity dispersion and nonlinear Kerr effects. Although an improvement in the performance of these optical links has been reported, the fixed residual dispersion per span (RDPS) that is typically used restricts the flexibility of link configurations. Thus, in this paper, a flexible dispersion-managed link configuration, comprising artificial distributions of linearly/nonlinearly incremented RDPS, is proposed. Simulations show that a descending distribution of RDPS before the midway OPC, and an ascending distribution of RDPS after the midway OPC, gives the best artificial distribution pattern as the number of fiber spans is increased, regardless of the RDPS incrementation method.

• Journal of the military operations research society of Korea
• /
• v.32 no.1
• /
• pp.176-187
• /
• 2006

It is difficult to estimate missile flight trajectory since a ballistic missile velocity is highly fast and has inherent behavior such as corkscrew due to unstable descending. This paper describes a comprehensive analysis of the flight trajectory characteristics of ballistic missiles. Various missile flight ranges based the comprehensive flight trajectory characteristics are derived by an analytical approach. It is shown analytically that threat due to the flight characteristics is significantly increased with reducing maximum missile ranges. This work is basic research of the establishment of operational concept for the lower tier missile defense system implementation.

• Journal of the Korean Wood Science and Technology
• /
• v.35 no.3
• /
• pp.22-28
• /
• 2007

Using woodceramics made from sawdust board of pine thinning logs, changes in surface temperature were investigated, by the heating rate and keeping time at maximum temperature. The heating rate of $2^{\circ}C/min$ and keeping time at maximum temperature 1 hour, were the highest in surface temperature. Also, it was found that woodcermics maintained heat for a long time because the descending velocity of their surface temperature was slower than that of the heater.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
• /
• 2008.04a
• /
• pp.15-18
• /
• 2008

A study on the fire and smoke behavior on experiments and analysis through STAR-CD in using about behavior analysis of the smoke. Kerosene of 3L in using on the experimental garden of 30cm in diameter same applies to heat release rate(HRR), buoyant force by Plume can be calculated at a rate of 1m/s. The result of experiment in average of velocity were 0.29m/s, and interpreted result were 0.28m/s. Besides, it is proved by interpreted that behavior of smoke movement can be not observed in the experiment. After smoke is Plume increased, ceiling-jet in formation being descend in smoke layer will be more thick smoke layer, and then vertical wall is collapsed in formation of wall-jet being descend. It is defined that smoke layer is more thick through descending course in wall-jet and ceiling-jet.

• Journal of Korea Foresty Energy
• /
• v.22 no.1
• /
• pp.24-29
• /
• 2003

Using woodceramics made from sawdust board of Larix leptolepis thinning logs, change in surface temperature were investigated, by the rate of resin impregnation and burning temperature. As the surface temperature of silicon rubber heater was going up, that of woodceramics also increase rapidly. Woodceramics made from under the condition of the rate of resin impregnation 70-80% and burning temperature 800-$1000^{\circ}C$, were higher than that of surface temperature. Also, it was found that woodceramics maintained heat for a long time because the descending velocity of their surface temperature was lower than that of the heater.

• Journal of information and communication convergence engineering
• /
• v.16 no.2
• /
• pp.67-71
• /
• 2018

The various techniques to compensate for the signal distortion due to the group velocity dispersion (GVD) and nonlinear Kerr effects of optical fibers in the optical links have been proposed in the literature. We propose a flexible dispersion-managed link configuration consisted of single-mode and dispersion-compensating fibers with irregular dispersion coefficients over all fiber spans, and an optical phase conjugator added midway along the optical links. By distributing the lengths of the single mode fibers, we achieve a flexible optical link. The simultaneous ascending and descending distribution of the single-mode fiber lengths before and after the optical phase conjugator, respectively, best compensates the distorted wavelength division multiplexed signals in the optical link with non-fixed coefficients. Our result is consistent with those of our previous work on fixed coefficients. Therefore, to improve the compensation at any magnitude of dispersion coefficient, we must artificially distribute the lengths of the single-mode fibers into a dispersion-managed link.

• Journal of Chest Surgery
• /
• v.54 no.2
• /
• pp.81-87
• /
• 2021

Background: Artificial grafts such as polyethylene terephthalate (Dacron) and expanded polytetrafluoroethylene (ePTFE) are used for various cardiovascular surgical procedures. The compliance properties of prosthetic grafts could affect hemodynamic energy, which can be measured using the energy-equivalent pressure (EEP) and surplus hemodynamic energy (SHE). We investigated changes in the hemodynamic energy of prosthetic grafts. Methods: In a simulation test, the changes in EEP for these grafts were estimated using COMSOL MULTIPHYSICS. The Young modulus, Poisson ratio, and density were used to analyze the grafts' material properties, and pre- and post-graft EEP values were obtained by computing the product of the pressure and velocity. In an in vivo study, Dacron and ePTFE grafts were anastomosed in an end-to-side fashion on the descending thoracic aorta of swine. The pulsatile pump flow was fixed at 2 L/min. Real-time flow and pressure were measured at the distal part of each graft, while clamping the other graft and the descending thoracic aorta. EEP and SHE were calculated and compared. Results: In the simulation test, the mean arterial pressure decreased by 39% for all simulations. EEP decreased by 42% for both grafts, and by around 55% for the native blood vessels after grafting. The in vivo test showed no significant difference between both grafts in terms of EEP and SHE. Conclusion: The post-graft hemodynamic energy was not different between the Dacron and ePTFE grafts. Artificial grafts are less compliant than native blood vessels; however, they can deliver pulsatile blood flow and hemodynamic energy without any significant energy loss.