• 대한의용생체공학회:의공학회지
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• 제43권5호
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• pp.319-330
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• 2022

In this study, the optimal driving frequency was derived through finite element analysis (FEA) to optimize the developed piezoelectric ultrasonic medical devices(PUMD) for bone surgery. The core of the PUMD is the piezoelectric ceramic (PZT), which is a vibrator that generates vibration energy. The piezoelectric ceramic shows the maximum current value with respect to the input voltage at the resonance frequency, which generates the maximum mechanical vibration. In the past, various studies have been conducted related to the analysis of PUMD, but most of the research so far has been limited to free vibration analysis. However, in order to derive the accurate resonant frequency, the initial stress generated by bolt tightening in the bolt-clamped Langevin type transducer (BLT) must be considered. In this study, after designing a PUMD, the driving performance according to the bolt tightening value was analyzed through FEA, and this was experimentally verified. First, the resonance mode and frequency response were confirmed through modal and harmonic analysis at 20-40 kHz, which is known as the optimal driving frequency band of PUMD for bone surgery. In addition, the design of the PUMD was confirmed by checking the mechanical behavior of the tip and the piezoelectric ceramic at the resonant frequency. Consequentially, the characteristic evaluation was performed, and it was confirmed that the resonant frequency result derived through the FEA was reasonable. Through this study, we presented a more rational FEA method than before for BLT transducers. We expect that this will shorten the time and cost of developing a PUMD, and will enable the development of more stable and high-quality products.

• 대한조선학회논문집
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• 제58권6호
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• pp.391-399
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• 2021

In order to investigate force and cavitation characteristics for the flat & twisted rudders in the Large Cavitation Tunnel (LCT), the rudder dynamometer was designed and manufactured. The measuring capacities of lift, drag and moment are ±1000 N, ±2000 N, and ±150 N-m, respectively. The present dynamometer uses the actuator with a harmonic drive to control the rudder angle without backlash. As the target ship is a military ship with twin shaft, each dynamometer was installed above the port & starboard rudders. After the installation of the model ship with all appendages, the model test composed of rudder force measurement and cavitation observation was conducted for the existing flat rudder & the designed twisted rudder. While the flat rudder showed the big difference of lift & moment between port & starboard, the twisted rudder presented a similar trend. The cavitation of the twisted rudder showed better characteristics than that of the flat rudder. Another set of model tests were conducted to investigate rudder performance by the change of the design propeller. There was little difference in rudder performance for the design propellers with slight geometric change. Through the model test, the characteristics of the flat & twisted rudders were grasped. On the basis of the present study, it is thought that the rudder with better performance would be developed.

• Steel and Composite Structures
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• 제41권6호
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• pp.873-886
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• 2021

In this paper, an analytical solution for thermodynamic response of functionally graded (FG) sandwich plates resting on variable elastic foundation is performed by using a quasi 3D shear deformation plate theory. The displacement field used in the present study contains undetermined integral terms and involves only four unknown functions with including stretching effect. The FG sandwich plate is considered to be subject to a time harmonic sinusoidal temperature field across its thickness with any combined boundary conditions. Equations of motion are derived from Hamilton's principle. The numerical results are compared with the existing results of quasi-3D shear deformation theories and an excellent agreement is observed. Several numerical examples for fundamental frequency, deflection, stress and variable elastic foundation parameter's analysis of FG sandwich plates are presented and discussed considering different material gradients, layer thickness ratios, thickness-to-length ratios and boundary conditions. The results of the present study reveal that the nature of the elastic foundation, the boundary conditions and the thermodynamic loading affect the response of the FG plate especially in the case of a thick plate.

• 한국엔터테인먼트산업학회논문지
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• 제14권3호
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• pp.229-236
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• 2020

본 논문에서는 우리나라의 국악기중 대표적인 관악기인 대금의 음색을 분석하였다. 대금은 크게 정악대금과 산조대금으로 구분하여 사용되고 있는데, 정악대금은 궁중음악과 풍류음악에서 연주되고 있으며, 산조대금은 산조, 시나위, 민속음악에서 주로 연주된다. 이렇게 2개의 대금이 서로 다른 음악장르에서 연주되고 있는 이유는 악기의 개량에 따른 것인데, 관의 길이와 지공의 위치를 조정하여 산조대금이 정악대금에 비하여 빠른 연주가 가능하게 되었고, 다양한 연주기법을 적용할 수 있게 되었으며, 음색의 차이를 만들어 냄으로써 음악과 조화로운 악기의 선택을 가능하게 하였다. 이번 실험에서는 정악대금과 산조대금을 같은 음을 연주하여 녹음한 결과를 바탕으로 배음의 구조와 음색의 특징을 분석하였으며, 이를 통해 저음이 풍부한 정악대금이 궁중음악 등 장중한 분위기의 곡에 조화로우며, 상대적으로 고음이 맑은 산조대금이 독주 등 밝은 음악에 잘 어울린다는 것을 알 수 있었다.

• 한국산업융합학회 논문집
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• 제25권3호
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• pp.423-431
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• 2022

The UPS(Uninterruptible Power Supply) system operates in the battery charging mode when the grid is normal, and in the UPS mode, which is the battery discharge mode when a grid error occurs. Since the UPS must supply the same voltage as the grid to the load within 4 [ms] in case of a grid error, the switching time and power recovery time should be short when controlling the output voltage and current of the UPS, and the power failure detection time is also important. The power outage detection algorithm using DFT(Discrete Fourier Transform) proposed in this paper compares the grid voltage waveform with the voltage waveform including the 9th harmonic generated through DFT using Schmitt trigger to detect power outage faster than the existing power outage monitoring algorithm. There are advantages. Therefore, it is possible to supply instant and stable power when switching modes in the UPS system. The multi-power-applied UPS system proposed in this paper uses DFT, which is faster than the conventional blackout monitoring algorithm in detecting power failure, to provide stable power to the load in a shorter time than the existing power outage monitoring algorithm when a system error occurs. The detection method was applied. The changeover time of mode switching was set to less than 4 [ms], which is 1/4 of the system cycle, in accordance with KSC 4310 regulation, which was established by the Industrial Standards Council on the regulation of uninterruptible power supply. A 10 [kW] UPS system in which commercial voltage, vehicle generator, and auxiliary diesel generator can be connected to each of the proposed transfer devices was constructed and the feasibility was verified by conducting an experiment.

• Composites Research
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• 제35권1호
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• pp.31-37
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• 2022

본 연구에서는 복합재료 블레이드의 최적 구조설계 프레임워크를 개발하고 이를 헬리콥터 블레이드에 적용하여 구조설계를 수행하였다. 개발된 최적 설계 프레임워크는 유전자 알고리즘과 입자 군집 최적화 알고리즘을 결합한 PSGA를 활용해 구성하였다. 이는 블레이드 단면에 대한 유한요소 모델 생성, 2차원 단면 유한요소 해석, 그리고 1차원 회전 보 해석의 단계를 거쳐 최적화 결과를 도출해낸다. 설계 과정에서 각 단면들은 B-spline으로 구성되며, 유한요소 생성 프로그램인 Gmsh를 활용해 모델링 된다. 이를 활용하여 최적화 과정에서 각 변수마다 대응되는 2차원 유한요소모델을 생성해 블레이드의 구조해석을 수행했다. 본 연구에서 제안한 프레임워크를 HART II 블레이드에 적용하여 최적 구조 설계를 수행했다. 최적 설계 결과 회전익 로터에서 요구하는 구조적 특징을 유지하면서, 공진회피와 질량 등의 조건이 개선된 블레이드 형상을 도출하였다.

• 한국공간구조학회논문집
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• 제22권3호
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• pp.49-56
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• 2022

Tuned mass damper (TMD) is widely used to reduce dynamic responses of structures subjected to earthquake loads. A smart tuned mass damper (STMD) was proposed to increase control performance of a traditional passive TMD. A lot of research was conducted to investigate the control performance of a STMD based on analytical method. Experimental study of evaluation of control performance of a STMD was not widely conducted to date. Therefore, seismic response reduction capacity of a STMD was experimentally investigated in this study. For this purpose, a STMD was manufactured using an MR (magnetorheological) damper. A simple structure presenting dynamic characteristics of spacial roof structure was made as a test structure. A STMD was made to control vertical responses of the test structure. Two artificial ground motions and a resonance harmonic load were selected as experimental seismic excitations. Shaking table test was conducted to evaluate control performance of a STMD. Control algorithms are one of main factors affect control performance of a STMD. In this study, a groundhook algorithm that is a traditional semi-active control algorithm was selected. And fuzzy logic controller (FLC) was used to control a STMD. The FLC was optimized by multi-objective genetic algorithm. The experimental results presented that the TMD can effectively reduce seismic responses of the example structures subjected to various excitations. It was also experimentally shown that the STMD can more effectively reduce seismic responses of the example structures conpared to the passive TMD.

• 한국산업융합학회 논문집
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• 제25권6_3호
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• pp.1239-1246
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• 2022

This paper introduces the effect of grease on the degradation characteristics of bearings used as key components of packaging equipment and automation systems. Bearings parts are installed to fix and support the rotating body of the system, and performance degradation of the bearings has a great effect on the life of the system too. When bearings are used in various devices and systems, the grease is applied to reduce friction and improve fatigue life. Determining the type of lubricant (grease) is important because it has a great influence on the operating environment and lifespan and ensures long lifespan of systems and facilities. However, studies that simultaneously compared and analyzed the change in mechanical degradation characteristics and the comparison of chemical degradation characteristics according to grease types under actual operating conditions are insufficient. In this paper, three types of small harmonic drive, high-load reducer, and low-load reducer grease used in power transmission joint modules are experimentally selected and finally injected into ball bearings with a load (19,500N) to improve bearing durability. Degradation characteristics were tested by attaching to test equipment. At this time, after the durability test under the same load conditions, the mechanical degradation characteristics, that is temperature, vibration according to the three greases types. In addition, the chemical degradation characteristics of the corresponding grease was compared to present the results of mutual correlation analysis.

• 한국구조물진단유지관리공학회 논문집
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• 제26권3호
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• pp.21-28
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• 2022

TMD는 다른 진동제어장치에 비해 구조가 단순하며, 구조물에 발생하는 정형화된 형태의 진동에 우수한 제어성능을 보인다. 그러나 다른 제어장치에 비하여 진동제어범위가 좁아 예상치 못한 외부하중으로 인하여 발생하는 진동주기에는 취약하다. 본 연구에서 개발된 ETMD는 Mass를 전자석으로 구성하여 전류를 공급할 때 자기장이 형성됨과 동시에 마찰판과의 마찰력을 상승시켜 Mass의 거동을 순간적으로 제어한다. 개발된 ETMD의 제어성능 평가를 위하여 모형 단순보 교량 중앙에 ETMD를 설치한 후 중앙부 최대 수직변위가 발생하는 3.02Hz 조건으로 강제 진동을 발생시켜 휨거동 제어실험을 수행하였다. 실험결과 ETMD는 중앙부 최대 수직변위가 발생하는 3.02Hz에서 변위 감쇠율이 57.51%로 우수한 제어성능을 발휘하며 그 외에 진동주기에도 안정적인 제어성능을 보이는 것을 확인하였다.

• International Journal of Internet, Broadcasting and Communication
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• 제14권3호
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• pp.249-257
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• 2022

In recent years, if we order food by easily accessing the online market with our smartphone, we can receive the product in a fresh state at dawn the next day. Cold chain is an industry that can create high added value because it has both the characteristics of general logistics and sensitivity to temperature. Based on the electrical specifications derived from the reefer container capacity requirement investigation, we proved that power supply to up to 33 reefer containers can be made by using three additional auxiliary power supplies which are applied for freight trains in Korea. In this paper, we conducted a research on a design of power supply system for freight train reefer container based on simulation as a basic research necessary for low-temperature distribution and cold chain construction based on the reefer container railroad. Consequently, the simulation was conducted using the three-phase inverter diagram in PSIM and the SVPWM (3-harmonic injection method) control technique, and it was verified that the required power voltage was satisfied with 622V_dc, which is lower than the input voltage of general SPWM of 718V_dc. The details of this paper could be used as a foundational study for constructing cold chains based on a reefer container dedicated to freight trains in the future.