• Smart Structures and Systems
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• 제6권5_6호
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• pp.579-593
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• 2010

Low-power radio frequency (RF) chip transceiver technology and the associated structural health monitoring platforms have matured recently to enable high-rate, lossless transmission of measurement data across large-scale sensor networks. The intrinsic value of these advanced capabilities is the allowance for high-quality, rapid operational modal analysis of in-service structures using distributed accelerometers to experimentally characterize the dynamic response. From the analysis afforded through these dynamic data sets, structural identification techniques can then be utilized to develop a well calibrated finite element (FE) model of the structure for baseline development, extended analytical structural evaluation, and load response assessment. This paper presents a case study in which operational modal analysis is performed on a three-span prestressed reinforced concrete bridge using a wireless sensor network. The low-power wireless platform deployed supported a high-rate, lossless transmission protocol enabling real-time remote acquisition of the vibration response as recorded by twenty-nine accelerometers at a 256 Sps sampling rate. Several instrumentation layouts were utilized to assess the global multi-span response using a stationary sensor array as well as the spatially refined response of a single span using roving sensors and reference-based techniques. Subsequent structural identification using FE modeling and iterative updating through comparison with the experimental analysis is then documented to demonstrate the inherent value in dynamic response measurement across structural systems using high-rate wireless sensor networks.

• 한국자동차공학회논문집
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• 제19권1호
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• pp.139-146
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• 2011

In present study, it aims to compare the noise and vibration characteristics between magnesium alloy and steel hood panel. The AZ31 magnesium hood panel was fabricated through warm forming process, and the noise and vibration characteristics between both hood panels was compared through the measurement of engine radiation noise and transmission loss, as well as FRF on modal analysis. The sound insulation performance of magnesium alloy was wholly superior to that of steel hood panel, even though the transmission loss of magnesium alloy is lower than that of steel due to mass effect primarily. The FRF characteristics on modal analysis indicates that the resonance frequency of magnesium hood panel is remarkably increased to higher value than that of steel hood panel. The radiation and interior noise of magnesium panel even without acoustic hood insulation were remarkably lower than those of steel hood panel with acoustic insulation, in particular, at a range below 4,000 rpm.

• The Journal of the Acoustical Society of Korea
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• 제28권3E호
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• pp.99-108
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• 2009

In this paper, we suggest criteria for objective measurement of speech quality in mobile VoIP (Voice over Internet Protocol) services over wireless mobile internet such as mobile WiMAX networks. This is the case that voice communication service is available under other networks. When mobile VoIP service users in the mobile internet network based on packet call up PSTN and mobile network users, but there have not been relevant quality indexes and quality standards for evaluating speech quality of mobile VoIP. In addition, there are many factors influencing on the speech quality in packet network. Especially, if the degraded speech with packet loss transfers to the other network users through the handover, voice communication quality is significantly deteriorated by the transformation of speech codecs. In this paper, we eventually adopt the Gilbert-Elliot channel model to characterize packet network and assess the voice quality through the objective speech quality method of ITU-T P. 862. 1 MOS-LQO for the various call scenario from mobile VoIP service user to PSTN and mobile network users under various packet loss rates in the transmission channel environments. Our simulation results show that transformation of speech codecs results in the degraded speech quality for different transmission channel environments when mobile VoIP service users call up PSTN and mobile network users.

• 설비공학논문집
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• 제17권4호
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• pp.325-332
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• 2005

This paper addresses the development of a scroll expander for power generation from relatively low temperature steam source. It has a double-sided orbiting scroll member so that no thrust bearing is needed to support the base plate of the orbiting scroll. Three power transmission shafts are placed at the periphery of the orbiting scroll base plate, and these shafts can also function as anti-rotation devices. Final output is obtained from the main central shaft engaged with the three power transmission shafts through gear assembly. The clearance between the fixed and orbiting scroll elements was estimated by comparing measurement of the mass flow rate with calculation results of a computer simulation. Due to large clearance, the expander total and volumetric efficiencies were measured to be $34\%\;and\;43\%$, respectively. It has been shown through the computer simulation that the total and volumetric efficiencies could be improved to $65\%\;and\;83\%$, respectively, if the current clearance is reduced by half.

• 한국기계가공학회지
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• 제12권6호
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• pp.69-76
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• 2013

This paper presents the development of the FCF method for the manufacturing of final products using numbers related to the minimum amount of work. The utilized product is a drum clutch, which is part of the transmission of an automobile. A double acting press is secured first and a prediction of the forming load on the practical material is made through an experiment with a plasticine model. Also, a finite element simulation using product shape and properties is performed, as well as a press experiment. A double acting press is manufactured that is suitable for a double acting experiment with a conventional hydraulic press(200 tons). A peripheral device for the press is additionally designed for experimental purposes. And, the press has as its essential points the drive speed, stroke control, etc., all of which influence the forming and is modified. Especially, a laser system is used for velocity measurement of two punches. The forming load of a practical material is predicted in order to derive a forming load formula for cold conditions on the basis of approximate similarity theory. Finite element analysis of the relative velocity ratio(RVR), etc., for most suitable flow defect(unfilling, etc.) prevention is achieved as well. The results are verified through a press experiment.

• 대한금속재료학회지
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• 제47권12호
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• pp.873-880
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• 2009

Water-vapor permeation through metallic barriers deposited on polymer substrates has been an important technological issue because the performance of the barrier is critical to the reliability of flexible organic devices. For the development of long-lifetime flexible organic devices, two different sets of samples were designed and demonstrated from the viewpoint of the water-vapor transmission rate (WVTR). Aluminum (Al) and polyethylene terephthalate (PET) were chosen for the barrier layer and the polymer substrate, respectively. Two stacking structures, a single-layer (Al/PET) structure and a double-layer (Al/PET/Al) structure, were used for the WVTR measurement. For the single-layer structure, the WVTR decreases as the thickness of the barrier layer increases. Compared to the single-layer sample, the double-layer sample showed superior WVTR performance (by nearly three times) when the total thickness of the Al barrier was greater than 100 nm.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.437-442
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• 2005

This paper deals with the measurement and analysis of radio characteristic of 424 MHz for using the automation of transmission and supply of electric power, ana automatic meter reading(AMR). Normally radio propagation characteristic is the base of system design, performance evaluation and choice of position of the base station in wireless communication. It is the most accurate way to design a base station through practical measurements, but it costs much time, money and engineers. So, we developed 424 MHz short range wave propagation model for AMR service.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 D
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• pp.2726-2728
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• 2005

The majority of sensors currently being used for measuring current need to contact with conductor carrying current. Therefore it is not easy to measure and insulate. In order to figure the solution out, the remote power measurement system is introduced in this paper. The system developed here enables us to measure the current of the commercial power without contact by using Rogowski Coil and wireless communication method. Measured current is processed for the wireless transmission, then is transferred to the computer through wireless receiver. The data arrived at the computer is displayed on the screen as waveform.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.629-633
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• 2006

We investigated a new longitudinal acceleration wave decomposition method in time domain. The proposed method separates up- and down-stream waves with an axial strain and axial acceleration measured at a single point on the transmission path. The advantages such as low computation load and easy implementation would be possible by developing time domain under the following assumptions; low frequency range, uniform cross sectional area and elastic wave propagation. We confirmed the feasibility and performance of the method through experiment using Split Hopkinson Pressure Bar (SHPB). The method can be effective in several applications, including active vibration control with wave view point, where real time wave decomposition is necessary.

• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2020년도 제62차 하계학술대회논문집 28권2호
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• pp.139-142
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• 2020

NB-IoT(Narrow Band Internet of Things) is an emerging LPWAN(Low Power Wide Area Network) radio technology. NB-IoT has many advantages like low power, low cost, and high coverage. However low bandwidth and low sampling rates also lead to poor positioning accuracy. This paper proposed a solution to optimize positioning accuracy under the OTDOA(Observed Time Difference of Arrival) approach by utilizing MLR(Multiple Linear Regression) models. Through the MLR model to predict the influence degree of weather(temperature, humidity, light intensity and air pressure) on the arrival time of signal transmission to improve the measurement accuracy. The improvement of measurement accuracy can greatly improve IoT applications based on NB-IoT.