• Structural Engineering and Mechanics
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• v.71 no.6
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• pp.751-761
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• 2019

Lamb wave technology is a promising technology in the field of structural health monitoring and can be applied in the detection and monitoring of defects in plate structures. Based on the reconstruction algorithm for the probabilistic inspection of damage (RAPID), a Lamb-based detection and evaluation method of through-thickness rectangular notches in metal plates was proposed in this study. The influences of through-thickness rectangular notch length and the angle between sensing path and notch length direction on signals were further explored through simulations and experiments. Then a damage index calculation method which focuses on both phase and amplitude difference between detected signals and baseline signals was proposed. Based on the damage index difference between two vertically crossed sensing paths which pass through the notch in a sensor network, the notch direction identification method was proposed. In addition, the notch length was determined based on the damage index distribution along sensing paths. The experimental results showed that the image reconstructed with the proposed method could reflect the information for the evaluation of notches.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.8
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• pp.33-41
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• 2021

Recently, many studies have been conducted on substituting fossil fuels with bio-refineries in existing industrial systems using biomass. Among the various bio-refineries, microalgae have received wide attention because it uses inorganic compounds to produce useful substances, which are extracted by a cell disruption process. Although numerous cell disruption methods exist, cell disruption efficiency has been studied by ultrasonic treatment. Ultrasound is a high-frequency (20 kHz or higher) sound wave and causes cell disruption by cavitation when passing through a solvent. In this study, we used the microalgal species Chlorella sp., which was cultured in a plate-type photobioreactor. The experiment was conducted using a continuous low-frequency processing device. The reduction of cells with time due to cell disruption was fitted using a logistic model, and optimum conditions for highly efficient cell disruption were determined by conducting experiments under multiple conditions.

• Steel and Composite Structures
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• v.50 no.1
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• pp.89-105
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• 2024

Multichannel analysis of surface waves (MASW) method has exhibited broad application prospects in the nondestructive detection of interfacial debonding in steel-concrete composite structures (SCCS). However, due to the structural diversity of SCCS and the high stealthiness of interfacial debonding defects, the feasibility of MASW method needs to be investigated in depth. In this study, synthetic parametric study on MASW nondestructive debonding detection for SCCSs is performed. The aim is to quantitatively analyze influential factors with respect to structural composition of SCCS and MASW measurement mode. First, stress wave composition and propagation process in SCCS are studied utilizing 2D numerical simulation. For structural composition in SCCS, the thickness variation of steel plate, concrete core, and debonding defects are discussed. To determine the most appropriate sensor arrangement for MASW measurement, the effects of spacing and number of observation points, along with distances between excitation points, nearest boundary, as well as the first observation point, are analyzed individually. The influence of signal type and frequency of transient excitation on dispersion figures from forwarding analysis is studied to determine the most suitable excitation signal. The findings from this study can provide important theoretical guidance for MASW-based interfacial debonding detection for SCCS. Furthermore, they can be instrumental in optimizing both the sensor layout design and signal choice for experimental validation.

• Korean Journal of Veterinary Research
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• v.33 no.4
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• pp.735-746
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• 1993

Electrocardiographic parameters of amplitude and the shape of waves on the unipolar precordial chest leads in the normal Korean native cattles have been measured with a 3 channel electrocardiograph built in a computed and analysis. The study was conducted on 98 heads of mean age of 17.6 months. The wave forms of P, T and QRS complex wave in all leads showed various types. The parameters of the amplitude in the wave types showed the most frequency in each lead that were analyzed as follow : 1. In P wave, amplitudes of positive type showed a frequency of 92.9% and 93.9% in leads $CV_6LU$ and $CV_6LL$ that were $83.8{\pm}31.0{\mu}V$ and $76.0{\pm}30.7{\mu}V$, and negative type showed a frequency of 97.9% in lead V 10 that were $-80.2{\pm}29.4{\mu}V$, respectively. But the plate type in leads $CV_6RU$ and $CV_6RL$ showed frequency of 48% and 58.3%, respectively. 2. Average amplitude of the QRS complex were in a range of $277.0{\pm}154.0{\mu}V$ to $648.2{\pm}146.2{\mu}V$(mean of $418.8{\pm}139.4{\mu}V$) in all leads that were manifested the Low-Voltage QRS complex(below 1 mV in unipolar precordial leads). Average amplitudes of each wave type in the QRS complex were $-250.0{\pm}139.8{\mu}V$ and $-399.2{\pm}226.8{\mu}V$ in the QS group types that showed a frequency of 50.0% and 82.5% in the leads $CV_6LU$ and $CV_6LL$, respectively. And average amplitudes of the R group types showed a frequency of 85.6%, 56.1% and 75.8% in the $CV_6RU$, $CV_6RL$ and $V_{10}$ that were $321.5{\pm}142.1{\mu}V$, $271.6{\pm}139.9{\mu}V$ and $552.4{\pm}132.7{\mu}V$, respectively. 3. In T waves, Amplitudes of the positive type showed a frequency of 60.2%, 46.9% and 83.7% in leads of $CV_6LL$, $CV_6RU$ and $CV_6RL$ that were respectively $184.7{\pm}93.7{\mu}V$ $103.7{\pm}64.43{\mu}V$ and $111.8{\pm}39.3{\mu}V$, the negative type showed a frequency of 62.2% and 93.7% in leads $CV_6LU$ and $V_{10}$ that were $142.2{\pm}82.1{\mu}V$ and $-280.3{\pm}107.2{\mu}V$, respectively. 4. Average amplitude of ST segment were $3.7{\pm}33.1{\mu}V$, $0.9{\pm}23.1{\mu}V$, $10.9{\pm}28.6{\mu}V$, $5.8{\pm}28.3{\mu}V$ and $-34.7{\pm}48.4{\mu}V$ in leads $CV_6LL$, $CV_6RU$, $CV_6RL$, $CV_6LU$ and $V_{10}$ respectively.

• Journal of the Korean earth science society
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• v.32 no.6
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• pp.674-686
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• 2011

Choosing a seismic source and geophone type including a coupling method can be the most important factor in shallow seismic surveys. We studied the characteristics of seismic signals by analyzing 6 different seismic data sets that collected from several sources and geophone conditions. Geophones attached to weight plate (1.8 kg) can be easily and economically installed on the paved road where geophones with spikes would cause the coupling problem. In addition, experiments in this study revealed that a small handy hammer can be used as a seismic source by striking the paved road to generate the seismic signals within 200 ms two-way travel time. Attaching weight plates to geophones may change the geophone response curve which generally depends on the geophone mass, but the change seems not to give significant differences in the first arrival of refracted wave and in the pattern of reflection events. Consequently, using weight plates on paved roads can be an efficient and cost-saving method in the near-surface high-resolution seismic surveys.

• Journal of the Korean Geotechnical Society
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• v.31 no.8
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• pp.17-28
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• 2015

The purpose of this study is to measure the volumetric water content of unsaturated soils during drying and wetting process by using volumetric pressure plate extractor (VPPE) incorporated with time domain reflectometry (TDR). The VPPE consists of a pressure cell, a pressure regulator, a burette system and a TDR probe. Two samples with different initial void ratios were prepared in the pressure cell, and the air pressure at the range of 0.1 kPa - 50 kPa was applied to adjust the matric suction by the pressure regulator. The burette system was used to measure the volumetric water content change of the sample according to the matric suction. In addition, the TDR probe, installed in the cell, was used to evaluate the dielectric constant from the reflected signal of the electromagnetic wave at the probe. The volumetric water content of specimen was estimated by the empirical equation between the volumetric water content and dielectric constant, which was calibrated with the Jumunjin sand. The test results show that the volumetric water content calculated by TDR probe is strongly correlated to the measured value by burette system. The hysteresis occurs during drying and wetting process. Furthermore, the degree of hysteresis reduces in the repeated process. This study suggests that TDR may be effectively used to evaluate the water content soil for the determination of water characteristic curve of unsaturated soils.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.37 no.2
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• pp.117-123
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• 2001

Anchovy scoop nets, a kind of lift net have been used in the coastal area of Cheju and South sea of Korea. An incandescent lamp(AC 100V, 1kW) is being used as a fishing lamp for gathering anchovy. Fishing lamp was installed at 1m ahead of the prow and 1.5m higher than the water surface. The fishing lamp let fish school rise to the water surface and attract to bag net. Accordingly, a successful anchovy catching depends on controling of fishing lamp. On the study, the distribution of spectral irradiance illumination of incandescent lamp(1kw) and the irradiance efficiency of reflection plate were analyzed and discussed to investigate the ability of fishing lamp which can attract anchovy school effectively. The results obtained are summarized as follows : 1. Around 180% of irradiance efficiency of incandescent lamp was increased by using the reflection plate. The light of lamp was radiated into water with circular shape. 2. The irradiance illumination of incandescent lamp in air was a maximum in wave length of 994nm but it was 690nm at 0.5m and 1.0m of water depth. 3. The relationship between water depth(x) and water illumination(y) of vertical light is represented as follows : y=146.03e supper(-0.37x) 4. The light of incandescent lamp(1kW) pass through much better into vertical direction than horizontal but it was estimated that the light was not able to reach depth of 20m.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.117-127
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• 2008

The volumetric pressure plate extractor (VPPE) was modified for the measurement of shear wave velocity ($V_s$) at various levels of matric suction as well as soil water characteristic curve (SWCC). A non-destructive technique with a pair of bender element (BE) was employed in order to measure the $V_s$ and the corresponding maximum shear modulus ($G_{max}$) of unsaturated soil specimens. Three types of soil were collected from different road construction sites in Korea. For all test soils, the variations in $G_{max}$ with the various levels of water content and matric suction were investigated using the developed apparatus. Compared with the preceding results from the suction-controlled torsional shear (TS) testing system and in-situ seismic tests, the feasibility fur evaluating modulus characteristics of unsaturated compacted soils with the developed VPPE-BE system was assessed. It was confirmed that the newly developed system would be potentially helpful in modeling seasonal variation of modulus.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.273-286
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• 2019

A derelict bridge called WoljungGyo was restored in Gyeongju, the capital city of ancient Silla. WoljungGyo was originally built in 760AD, and later rebuilt in 1280AD during the Goryeo Kingdom. The bridge lasted in working condition for at least 520 years. The bridge was uncovered to the remains of both abutments and four piers, with only one or two steps remaining. One of the foundation for piers showed evidence of partial settlement. The cause of the partial settlement is important for the successful restoration of the bridge so that an extensive investigation was carried out, which includes layer stratification by boring, 2-D stiffness profiling by surface-wave tests, and large scaled-plate load test for evaluating capacity. In addition to the field studies in the Woljunggyo bridge, 3-D finite element analysis was also conducted. Based on the results of the site investigation and the numerical analysis, it was concluded that the further ground improvement to build the piers was not necessary so that the gravels were placed and leveled underneath the existing pier stones to compensate partial settlement before the restoration.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.63-71
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• 2018

A flower support was developed for real flower decoration automation production system using an ultrasonic wave sealer to automatically produce a system. Because a flower support for real flower decoration that was produced manually could not meet the needs of the consumers, this study developed an automated manufacturing system to increase productivity. A flower support for real flower decoration was constructed using a cap consisting of plastic and plate made from non-woven fabric. The guide was designed to transport the cap to the ultrasonic wave sealer and optimal guide was developed from the test according to the material and shape. To produce the entire system, the guides and accessories were weighed and appropriate motors and pulleys were calculated. Control of the automation production system was based on a PCB board, which increased the reliability and security, and a remote controller with manual and automatic modes was prepared. After development, tests of the transfer precision and repetition accuracy revealed an X-axis of 2.7mm, a Y-axis of 1 mm, and a repetition of 0 mm. The productivity was also checked. The automated machine worked 8 hours/day to make 35 supports and 70 Therefore, the automatic system produces 200% more output than manual work