• Journal of Engineering Education Research
• /
• v.27 no.4
• /
• pp.21-27
• /
• 2024

This study introduces a series of processes aimed at understanding the noise characteristics generated by jet engines and devising measures to mitigate them through interdisciplinary capstone design projects. During the project execution, educational methods were applied to foster 4Cs (creativity, communication, collaboration, critical thinking) competencies. Project objectives were set through team discussions, and individual team members were assigned primary roles to act as subgroup leaders. As a result, the project was executed as follows: combustion tests were conducted using an SR-30 turbojet engine to generate noise, and the locations and characteristics of the noise sources were identified using beamforming techniques and frequency analysis applied to a 30-microphone array. Additionally, chevron nozzles were designed and fabricated to confirm their noise reduction performance.

• Smart Structures and Systems
• /
• v.17 no.6
• /
• pp.859-880
• /
• 2016

This study aims to establish an effective methodology for the detection of instant damages occurred in cable-stayed bridges with the measurements of cable vibration and structural temperatures. A transfer coefficient for the daily temperature variation and another for the long-term temperature variation are firstly determined to eliminate the environmental temperature effects from the cable force variation. Several thresholds corresponding to different levels of exceedance probability are then obtained to decide four upper criteria and four lower criteria for damage detection. With these criteria, the monitoring data for three stay cables of Ai-Lan Bridge are analyzed and compared to verify the proposed damage detection methodology. The simulated results to consider various damage scenarios unambiguously indicate that the damages with cable force changes larger than ${\pm}1%$ can be confidently detected. As for the required time to detect damage, it is found that the cases with ${\pm}2%$ of cable force change can be discovered in no more than 6 hours and those with ${\pm}1.5%$ of cable force change can be identified in at most 9 hours. This methodology is also investigated for more lightly monitored cases where only the air temperature measurement is available. Under such circumstances, the damages with cable force changes larger than ${\pm}1.5%$ can be detected within 12 hours. Even though not exhaustively reflecting the environmental temperature effects on the cable force variation, both the effective temperature and the air temperature can be considered as valid indices to eliminate these effects at high and low monitoring costs.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.3
• /
• pp.159-169
• /
• 2004

In this study, integration control of air-cell seat and semi-active suspension is proposed to minimize the road-tyre force which can cause uncomfortable feeling to rider. The proposed integration control with sliding perturbation observer is consisted of air-cell seat control which uses the force generated by air-cell and the sky-hook control. The air-cell seat itself has been modeled as a 1 degree of freedom spring-damper system. The actual characteristics of the air-cell have been analyzed through experiments. In this paper, we introduces a new robust motion control algorithm using partial state feedback for a nonlinear system with modelling uncertainties and external disturbances. The major contribution of this work is the development and design of robust observer for the state and the perturbation. The combination skyhook controller and air-cell controller using the observer improves control performance, because of the robust routine called Sliding Observer Design for Integration Control of Air-Cell Seat and Semi-active Suspension. The simulation results show a high accuracy and a good performance.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.12
• /
• pp.3533-3539
• /
• 2009

An air conditioner impeller has been used to suck the warm air and to blow the chilled air by the centrifugal force induced from the rotation of it. To check the possibility of the fracture due to resonance, both numerical and experimental approach was carried out. For the structural analysis, the commercial code ANSYS based on the Finite Element Method was employed. The possibility of the fracture is the resonance between the natural frequency of impeller and characteristic frequency due to the aerodynamic forces. Experiment was carried out to see the natural frequency and numerical analysis based on the Vortex Element Method is performed to get the characteristic frequency. Comparing the natural frequencies that are calculated as described, we believe that resonance occurs.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.45 no.3
• /
• pp.31-39
• /
• 2022

The Army, Navy, and Air Force are currently making various efforts to apply defense IoT technology by reflecting the characteristics of each military. However, there are concerns that comprehensive collection, management, and analysis may be limited because each military has no overlapping system or guaranteed interoperability of data, and there are inefficient aspects in terms of using and investing a limited defense budget. In this study, evaluation items and priorities for pilot projects were selected by applying Delphi technique and AHP method to determine which projects are preferentially effective when commonly applied in terms of Army, Navy, and Air force. As a result of the analysis, the project basis and driving force, project feasibility, performance and ripple effect, redundancy and connection were identified in the order of IoT-based small detachment units and unmanned base construction, intelligent smart unit, smart ground ammunition depot, and smart training management system. According to the comprehensive results reflecting the weights of each evaluation item, the fact that small detachment units and unmanned base construction project are recognized as the first project to be applied to the Army, Navy, and Air Force is a valid approach to be effective while each military is burdened with personnel management because of the reduction of manpower. Through the research results, it is expected that the direction of application to the policy of the defense IoT project can be confirmed in terms of efficient use of limited budgets.

• Journal of the Society of Disaster Information
• /
• v.18 no.2
• /
• pp.241-251
• /
• 2022

Purpose: In the event of a fire in a high-rise building, if the smoke control area is not effectively protected, smoke or flames enter the stairwell, making it difficult to evacuate. When inflowing air is discharged from a closed corridor, a negative pressure is formed in the corridor, the pressure in the smoke control area becomes excessively high, and the force required to open the door during evacuation is exceeded. Also, if the air introduced into the hallway is not exhausted, the smoke may flow back into the smoke control area. This paper tried to identify the problems caused by the inflowing air and to find out how to improve the performance. Method: Using the CONTAM program, simulations were performed with the basic conditions and the modified conditions. Result: If the inflowing air was discharged from the sealed corridor, overpressure occurred in the Smoke Control Area and exceeded the opening force, and the prevent smoke backflow was insufficient in the layer where the inflowing air was not discharged. Conclusion: "Differential pressure exhaust damper" application, simultaneous opening of two exhaust dampers, and automatic window installation between corridors and outdoors improved the exhaust performance of inflowing air.

• Journal of the Society of Disaster Information
• /
• v.17 no.4
• /
• pp.829-838
• /
• 2021

Purpose: The Air Spring Damper System (ASDS) is proposed when existing concrete structures that have not been seismic resistant for economic and technical reasons or low-rise concrete structures that are difficult to earthquake. Method: To conduct a study on the damping force antigen in the kinetic equation of free vibration, we analyze whether this device has damping ability as a damper experimentally and theoretically, and examine the possibility of field application. Result: The air damper system is considered to be more economical than steel hysteresis dampers even if the number of dampers increases due to its easy manufacture and construction and low restrictions on shape, size, material, etc. Conclusion: In an air spring damper system, it is essential to reduce the diameter of the air inlet/outlet hole to improve the damping ratio, and in this case, if the diameter exceeds a certain lower limit, consideration of the compressibility of air is required, so further research is needed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.30 no.4
• /
• pp.195-203
• /
• 2018

Mohair is widely used as an airtight material for filling the gap between a window frame and sash. The purpose of this study is to investigate infiltration rate and opening force of sliding windows according to the mohair installation conditions. Infiltration experimental apparatus was set up, and the experimental results were applied to windows to find a correlation between infiltration rates and opening forces. When 4 rows of mohair were installed, the infiltration rate increase became 27.1% per clearance length increase of 1 mm, and the infiltration rate decrease became 5.7% per shortened length increase of 0.1 mm. For 4 rows of mohair, the opening force decreased by 28.2% as the clearance increased by 1 mm, and it increased by 9.3% as the shortened length increased by 0.1 mm.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.3
• /
• pp.952-957
• /
• 2015

Recently, the interior permanent magnet (IPM) motors for electric vehicle (EV) traction motor are being extensively researched because of its high energy density and high efficiency. The traction motor for EV requires high power and high efficiency at the wide driving region. Therefore, it is essential to fully consider the characteristics of the motor from low speed to high-speed driving regions. Especially, when the motor is driven at high speed, a significant centrifugal force is applied to the rotor. Thus, the rotor must be stably structured and be fully endured at the critical speed. In this paper, aims to examine the characteristics of the IPM motor by adjusting the width of air-barrier according to the permanent magnet position which is critical in designing an IPM motor for EV traction motors and to conduct a centrifugal force analysis for grasping mechanical safety.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.359-359
• /
• 2014

In this study, surface plasmon resonance structures for the selective and the enhanced transmission of infrared light were designed. In order to relieve the large discontinuity of refractive index between air and metal hole array, $Si_3N_4$ was used as the impedance matching layer. Experimental parameter were calculated and determined in advance by the rigorous coupled wave analysis (RCWA) simulation, and then the experiment was carried out. A 2-dimensional metal hole array structures were patterned on the size of $1{\times}1cm^2$ GaAs substrate using photolithography process, and 5 nm thick Ti, 50 nm thick Au were deposited by E-beam evaporator, respectively. Subsequently, $Si_3N_4$ films with various thicknesses (150, 350, 550, and 750 nm) were deposited by plasma enhanced chemical vapor deposition (PECVD). For the comparison, transmittance of specimens with and without $Si_3N_4$ was measured using Fourier transform infrared spectroscopy (FTIR) in the range of $2.5-15{\mu}m$. Furthermore, the surface and the cross-sectional images were collected from the specimens by scanning electron microscopy (SEM). From the results, it was demonstrated that the transmittance was enhanced up to 80% by the deposition of 750 nm $Si_3N_4$ at $6.23{\mu}m$. It has advantage of enhanced transmission despite the simple fabrication process.