• Wind and Structures
• /
• v.25 no.3
• /
• pp.233-259
• /
• 2017

Investigations on simulated near-surface atmospheric boundary layer (ABL) in an open-jet facility are carried out by conducting experimental tests on small-scale models of low-rise buildings. The objectives of the current study are: (1) to determine the optimal location of test buildings from the exit of the open-jet facility, and (2) to investigate the scale effect on the aerodynamic pressure characteristics. Based on the results, the newly built open-jet facility is well capable of producing mean wind speed and turbulence profiles representing open-terrain conditions. The results show that the proximity of the test model to the open-jet governs the length of the separation bubble as well as the peak roof pressures. However, test models placed at a horizontal distance of 2.5H (H is height of the wind field) from the exit of the open-jet, with a width that is half the width of the wind field and a length of 1H, have consistent mean and peak pressure coefficients when compared with available results from wind tunnel testing. In addition, testing models with as large as 16% blockage ratio is feasible within the open-jet facility. This reveals the importance of open-jet facilities as a robust tool to alleviate the scale restrictions involved in physical investigations of flow pattern around civil engineering structures. The results and findings of this study are useful for putting forward recommendations and guidelines for testing protocols at open-jet facilities, eventually helping the progress of enhanced standard provisions on the design of low-rise buildings for wind.

• Steel and Composite Structures
• /
• v.27 no.4
• /
• pp.427-438
• /
• 2018

In this paper, the single and multi-objective optimization of thin-walled conical tubes with different types of indentations under axial impact has been investigated using surrogate models called metamodels. The geometry of tapered thin-walled tubes has been studied in order to achieve maximum specific energy absorption (SEA) and minimum peak crushing force (PCF). The height, radius, thickness, tapered angle of the tube, and the radius of indentation have been considered as design variables. Based on the design of experiments (DOE) method, the generated sample points are computed using the explicit finite element code. Different surrogate models including Kriging, Feed Forward Neural Network (FNN), Radial Basis Neural Network (RNN), and Response Surface Modelling (RSM) comprised to evaluate the appropriation of such models. The comparison study between surrogate models and the exploration of indentation shapes have been provided. The obtained results show that the RNN method has the minimum mean squared error (MSE) in training points compared to the other methods. Meanwhile, optimization based on surrogate models with lower values of MSE does not provide optimum results. The RNN method demonstrates a lower crashworthiness performance (with a lower value of 125.7% for SEA and a higher value of 56.8% for PCF) in comparison to RSM with an error order of $10^{-3}$. The SEA values can be increased by 17.6% and PCF values can be decreased by 24.63% by different types of indentation. In a specific geometry, higher SEA and lower PCF require triangular and circular shapes of indentation, respectively.

• Korean Journal of Optics and Photonics
• /
• v.25 no.4
• /
• pp.200-206
• /
• 2014

In this paper, using the value theoretically calculated to emit multidirectionally a beam coming into an optical fiber with diameter of $125{\mu}m$, we modeled and produced a cone-shaped structure at the distal end of the fiber. A numerical simulation was performed for an optical fiber tip in which all incident beams were totally reflected and emitted toward the side, as well as for an optical fiber tip from which the beams could be emitted forward and sideways simultaneously. We produced multidirectional-firing optical fiber tips based on the simulation result and model. Laser fabrication of the optical fiber was done by processing a cone-shaped structure at the distal end of an optical fiber with diameter of $125{\mu}m$ using a femtosecond pulsed laser and polishing the processed surface with a $CO_2$ laser. We also conducted an analysis to compare experimental and simulation results.

• Korean Journal of Food Science and Technology
• /
• v.41 no.4
• /
• pp.369-373
• /
• 2009

${\alpha}$-Waxy corn starch was used as a feed for twin-screw extrusion in order to enhance starch liquefaction with added thermostable ${\alpha}$-amylase (derived from Bacillus licheniformis). The residence time distribution and starch liquefaction were investigated. The starch liquefaction was analyzed in terms of reducing sugar contents, molecular size from gel permeation chromatography (GPC), and microstructure from scanning electron microscopy (SEM). The use of ${\alpha}$-starch contributed to the production of more reducing sugar than the use of raw starch use alone. From GPC, the effect of ${\alpha}$- starch on the molecular size reduction was shown to be small. From SEM, irregular and damaged surface were observed on the extrudate from ${\alpha}$-starch, as compared to those from raw starch. The spread of residence time distribution curves was greater with feed of ${\alpha}$-starch than raw starch, indicating that ${\alpha}$-starch was hard to flow forward during extrusion. This could be improved by increasing the feed moisture content and barrel temperature of extruder.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.20 no.11
• /
• pp.2162-2166
• /
• 2016

This paper describes the implementation of AUSV system for sonar image acquisition to survey the seabed. The system is controlled by Feed Forward PID algorithm on the vessel for bearing of the thrusters composed of motion sensor and DGPS which calculates the differences between the current location and the destination location for longitude and latitude based on GPS coordinates. As experimental results, the bearing control performance is good that the error distance from the destination positions are under 6m in total survey track of 1km. And the sonar image deviation of a object is under 12 pixels from the manned survey method, which the comparison with the total image quality is almost the same as the manned survey one. Thus the proposed AUSV system is a new method of system can be utilized at the limited survey areas as the surveyor should not be able to approach on sea surface by onboard vessel.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.5
• /
• pp.2985-2992
• /
• 2015

In this study, the characteristics of heat transfer and pressure drop was theoretically analyzed by changing longitudinal pitch, bump phase, location of vortex generator about the staggered tube banks by applying SST (Shear Stress Transport) turbulence model of ANSYS FLUENT v.14. Before carrying out CFD (Computational Fluid Dynamics) analysis, It is presumed that the boundary condition is the tube surface temperature of 363 K, the inlet air temperature of 313 K and the inlet air velocity of 5-10 m/s. The results indicated that the heat transfer coefficient is not affected by the longitudinal pitch and the bump phase of circle type was more appropriate than serrated type in the characteristics of heat transfer and pressure drop. Additionally, in case of vortex generator location, the heat transfer characteristics showed that forward location of tube was more favorable 4.6% than backward location.

• Geophysics and Geophysical Exploration
• /
• v.1 no.1
• /
• pp.71-78
• /
• 1998

Inversion schemes of 2-D MT survey data generally take enormous computational time and computer memory. In addition, careful attention must be paid in handling MT data, especially in cases of TM mode, inversion results can be seriously distorted because of static effect caused by current channeling across inhomogeneous surface boundaries. There-fore inversion algorithm using the GRRI scheme for TM mode MT data was implemented. This scheme is based on a perturbation analysis with a locally 2-D analysis and local inversions were sequently performed over each divided section without additional forward modelings. The algorithm was applied to several synthetic data for the purpose of verification of its efficiency and applicability. With less computer resources than conventional schemes, it could handle static effect directly by including current channeling across inhomogeneous boundaries. Thus it is expected to be used for an useful tool such as a real-time inversion scheme in the field.

• Journal of Biosystems Engineering
• /
• v.43 no.4
• /
• pp.273-284
• /
• 2018

Purpose: Conventional headland turning typically requires repeated forward and backward movements to move the farming equipment to the next row. This research focuses on developing an upland agricultural robot with an optimized headland turning mechanism that enables a $180^{\circ}$ turning positioning to the next row in one steering motion designed for a two-wheel steering, four-wheel drive agricultural robot named the HADA-bot. The proposed steering mechanism allows for faster turnings at each headland compared to those of the conventional steering system. Methods: The HADA-bot was designed with 1.7-m wide wheel tracks to travel along the furrows of a garlic bed, and a look-ahead path following algorithm was applied using a real-time kinematic global positioning system signal. Pivot turning tests focused primarily on accuracy regarding the turning radius for the next path matching, saving headland turning time, area, and effort. Results: Several test cases were performed by evaluating right and left turns on two different surfaces: concrete and soil, at three speeds: 1, 2, and 3 km/h. From the left and right side pivot turning results, the percentage of lateral deviation is within the acceptable range of 10% even on the soil surface. This U-turn scheme reduces 67% and 54% of the headland turning time, and 36% and 32% of the required headland area compared to a 50 hp tractor (ISEKI, TA5240, Ehime, Japan) and a riding-type cultivator (CFM-1200, Asia Technology, Deagu, Rep. Korea), respectively. Conclusion: The pivot turning trajectory on both soil and concrete surfaces achieved similar results within the typical operating speed range. Overall, these results prove that the pivot turning mechanism is suitable for improving conventional headland turning by reducing both turning radius and turning time.

• Wind and Structures
• /
• v.34 no.5
• /
• pp.395-405
• /
• 2022

Tornado-induced damages to high-rise buildings and low-rise buildings are quite different in nature. Tornado losses to high-rise buildings are generally associated with building envelope failures while tornado-induced damages to low-rise buildings are usually associated with structural or large component failures such as complete collapses, or roofs being torn off. While studies of tornado-induced structural damages tend to focus mainly on low-rise residential buildings, transmission towers, or nuclear power plants, the current rapid expansion of city centers and development of large-scale building complexes increases the risk of tornadoes impacting tall buildings. It is, therefore, important to determine how tornado-induced load affects tall buildings compared with those based on synoptic boundary layer winds. The present study applies an experimentally simulated tornado wind field to the Commonwealth Advisory Aeronautical Research Council (CAARC) building and estimates and compares its pressure coefficient effects against the Atmospheric Boundary Layer (ABL) flow field. Simulations are performed at the Wind Engineering, Energy and Environment (WindEEE) Dome which is capable of generating both ABL and tornadic winds. A model of the CAARC building at a scale of 1:200 for both ABL and tornado flows was built and equipped with pressure taps. Mean and peak surface pressures for TLV flow are reported and compared with the ABL induced wind for different time-averaging. By following a compatible definition of the pressure coefficients for TLV and ABL fields, the resulting TLV pressure field presents a similar trend to the ABL case. Also, the results show that, for the high-rise building model, the mean and 3-sec peak pressures are larger for the ABL case compared to the TLV case. These results provide a way forward for the code implementation of tornado-induced pressures on high-rise buildings.

• The korean journal of orthodontics
• /
• v.52 no.5
• /
• pp.313-323
• /
• 2022

Objective: This study aimed to estimate the clinical effects of different types of bone-anchored maxillary protraction devices by using a network meta-analysis. Methods: We searched seven databases for randomized and controlled clinical trials that compared bone-anchored maxillary protraction with tooth-anchored maxillary protraction interventions or untreated groups up to May 2021. After literature selection, data extraction, and quality assessment, we calculated the mean differences, 95% confidence intervals, and surface under the cumulative ranking scores of eleven indicators. Statistical analysis was performed using R statistical software with the GeMTC package based on the Bayesian framework. Results: Six interventions and 667 patients were involved in 18 studies. In comparison with the tooth-anchored groups, the bone-anchored groups showed significantly more increases in Sella-Nasion-Subspinale (°), Subspinale-Nasion-Supramentale(°) and significantly fewer increases in mandibular plane angle and the labial proclination angle of upper incisors. In comparison with the control group, Sella-Nasion-Supramentale(°) decreased without any statistical significance in all treated groups. IMPA (angle of lower incisors and mandibular plane) decreased in groups with facemasks and increased in other groups. Conclusions: Bone-anchored maxillary protraction can promote greater maxillary forward movement and correct the Class III intermaxillary relationship better, in addition to showing less clockwise rotation of mandible and labial proclination of upper incisors. However, strengthening anchorage could not inhibit mandibular growth better and the lingual inclination of lower incisors caused by the treatment is related to the use of a facemask.