• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1127-1131
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• 2005

One of problems in industries is an installation for an automation system device such sensor, transducer, controller, and so on those are located in different areas. Such problem makes a difficulty for maintenance and installation. The aim of this research attempts to design a high performance controller with remote devices. One attractive is to group near devices in near place together to centralizes control. This paper presents network device groups distributed through digital and analog Remote Terminal Unit (RTUs). Such devices are centralized by computer or PLC control and communicated with similar protocol through serial bus. Our scheme, there are many advantages such as, saving both time and cost,convenience compared to other ways.

• Smart Structures and Systems
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• 제12권5호
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• pp.547-577
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• 2013

To suppress vibration and noise of mechanical structures piezoelectric ceramics play an increasing role as effective, simple and light-weighted damping devices as they are suitable for sensing and actuating. Out of the various piezoelectric damping methods this paper compares mode based active control strategies to passive shunt damping for thin plates. Therefore, a new approach for the optimal placement of the piezoelectric sensors/actuators, or more general transducers, is proposed after intense theoretical investigations based on the Kirchhoff kinematical hypotheses of plates; in particular, modal and nilpotent transducers are discussed in detail. Based on the proposed distribution a discrete design for modal transducers is implemented, tested and verified on an experimental setup. For active control the modal sensors clearly identify the eigenmodes, whereas the modal actuators impose distributed eigenstrains in order to reduce the transverse plate vibrations. In contrast to the modal control, passive shunt damping works without requiring additional actuators or auxiliary power and can therefore act as an autonomous system, but it is less effective compensating the flexible vibrations. Exemplarily, an acryl glass plate disturbed by an arbitrary force initialized by a loudspeaker is investigated. Comparing the different methods their specific advantages are highlighted and a significant broadband reduction of the vibrations of up to -20dB is obtained.

• 수산해양기술연구
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• 제46권3호
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• pp.248-256
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• 2010

Acoustic side-aspect target strength (TS) of living Japanese anchovy (Engraulis japonicus) was measured at 120kHz during in situ experiments. The data were collected by lowering and horizontally projecting the splitbeam transducer into the anchovy school. For analysis and interpretation of the side-aspect TS data, acoustic theoretical model, based on the fish morphology, and dorsal-aspect TS data were used. Total length of the anchovy ranged from 6.6 to 12.8cm (mean length 9.3cm). The side-aspect TS distributed between -40 and -55dB, has an obvious length dependency. The mean side-aspect TS of the anchovy was -47.8dB, and the TS was about 2dB higher than mean TS generated from dorsal-aspect measurements. With reference to maximum TS, the results of the side-aspect TS were distributed within the range of the theoretical and dorsal-aspect TS. Apparently these tendency indicates that side-aspect TS measured from the study is useful data. These in situ measurements of side-aspect TS can be applied to improve acoustic detection and estimates of the anchovy, and is necessary to measure with a various frequency and length for making enhance data.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 학술발표대회 논문집 제17권 2호
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• pp.259-262
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• 1998

In this paper, we have studied measurement technique for inhomogeneous residual stress using acoustic microscopy with quadrature detector. In experiment, aluminum tensile specimen with the flaw has been made and loaded by Instrone. A spherical typed acoustic transducer of center frequency 5MHz has been used for sending a longitudinal acoustic wave into a stressed specimen. It has been shown in experimental results that the phase has largely changed around the flaw that residual stress has been largely distributed and acoustic microscopy has been used in the field of residual stress measurement.

• 대한기계학회논문집A
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• 제30권9호
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• pp.1160-1165
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• 2006

In this paper, the 2-dimensional uniaxial force sensors array is introduced to detect the distributed force using fiber Bragg gratings. Uniaxial force transducer was designed to avoid the chirping and micro bending which degrade the performance of the sensor. The Brags wavelength shift of the sensor was estimated using the finite element analysis. Using this uniaxial force sensor, the uniaxial force sensors array $(3{\times}3)$ was fabricated, and the Performance of this sensors array was evaluated. The Presented sensors may has very simple configuration and its wiring is very simple compared with any other force sensors arrays.

• ALGAE
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• 제23권1호
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• pp.83-90
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• 2008

Eelgrass beds are very productive and provide nursery functions for a variety of fish and shellfish species. Management for the conservation of eelgrass beds along the Korean coasts is critical, and requires comprehensive strategies such as vegetation mapping. We suggest a mapping method to spatial distribution and quantify of eelgrass beds using a digital echosounder. Echosounding data were collected from the northeast part of Kwangyang Bay, on the south of Korea, in March, 2007. A transducer was attached to a boat equipped with a DGPS. The boat completed a transect survey scanning whole eelgrass beds of 11.7 km2 with a speed of 1.5-2 m s-1 (3-4 knot). The acoustic reflectivity of eelgrass allowed for detection and explicit measurements of canopy cover and height. The results showed that eelgrass bed was distributed in depth from 1.19 to 3.6 m (below MSL) and total dry weight biomass of 4.1 ton with a vegetation area of 4.05 km2. This technique was found to be an effective way to undertake the patch size and biomass of eelgrass over large areas as nondestructive sampling.

• International Journal of Aeronautical and Space Sciences
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• 제15권1호
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• pp.1-19
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• 2014

Attaching a piezoelectric transducer to a vibrating structure, and shunting it with an electric circuit, gives rise to different passive, semi-passive, and semi-active control techniques. This paper attempts to review the research related to structural vibration control, via passive, semi-passive, and semi-active control methods. First, the existing electromechanical modeling is reviewed, along with the modeling methods. These range from lumped parameters, to distributed parameters modeling of piezostructural systems shunted by electrical networks. Vibration control laws are then discussed, covering passive, semi-passive, and semi-active control techniques, which are classified according to whether external power is supplied to the piezoelectric transducers, or not. Emphasis is placed on recent articles covering semi-passive and semi-active control techniques, based upon switched shunt circuits. This review provides the necessary background material for researchers interested in the growing field of vibration damping and control, via shunted piezostructural systems.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.27-31
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• 2003

Underwater acoustic navigation systems are classified into three systems: ultra-short baseline (USBL), short baseline (SBL), and long baseline (LBL). Because the USBL system estimates the angle of a submersible, the estimation error becomes large if the submersible is far from the USBL transducer array mounted under a support vessel. SBL and LBL systems estimate submersible's location more accurately because they have wider distribution of measuring sensors. Especially LBL systems are widely used as a navigation system for deep ocean applications. Although it is most accurate system it still has estimation errors because of noise, measurement error, refraction and multi-path of acoustic signal, or wrong information of the distributed transponders. In this paper the estimation error of the LBL system are analyzed from a point of sensitivity. It is assumed that the error exists only in the distance between a submersible and the transponders. For this purpose sensitivity of the estimated position with respect to relative distances between them is analyzed. The result says that estimation error is small if the submersible is close to transponders but not near the ocean bottom.

• 한국지반공학회지:지반
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• 제13권6호
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• pp.13-24
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• 1997

화강풍화토는 국내 지반의 2/3이상을 차지할 정도로 광범위하게 분포하며 도로, 지하철, 사면조성, 건물의 기초설치 등 여러 건설현장에서 빈번히 접할 수 있다. 화강풍화토의 입자구조는 풍화정도와 모암의 구성광물에 의해 영향을 받고 특히 보통의 구속 암에서도 입자 파쇄가 발생하며 비교란 지반의 특성과 다짐토 지반의 특성이 큰 차이가 있다. 본 연구에서는 현장에서 직접 삼축시험용 비교란 화강풍화토시료를 채취할 수 있는 시료채취기를 개발하였고 이를 이용하여 채취한 비교란 시료와 정적으로 다져진 시료에 대하여 공진주/비틂 전단시험과 삼축압축시험을 수행하였다. 시험결과로부터 미소한 변형률에서의 거동특성과 비교란 및 다짐 화강풍화토의 강도특성을 검토하였다. 대상으로 한 지반의 경우 1% 이내의 미소한 변형률 영역에서는 다짐시료와 비교란시료의 탄성계수가 거의 일치하였으며 강도의 뚜렷한 차이 또한 발견할 수 없었다. 비교란화강풍화토의 경우는 시료의 불균일성 등으로 인하여 파괴시의 변형률이 매우 넘게 분포하였다.

• 비파괴검사학회지
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• 제34권3호
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• pp.211-219
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• 2014

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.