• Steel and Composite Structures
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• v.34 no.6
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• pp.837-851
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• 2020

This study aims to examine the interface shear behavior between precast high-strength concrete slabs with pockets and steel beam to achieve accelerated bridge construction (ABC). Twenty-six push-out specimens, with different stud height, stud diameter, stud arrangement, deck thickness, the infilling concrete strength in shear pocket (different types of concrete), steel fiber volume of the infilling concrete in shear pocket concrete and casting method, were tested in this investigation. Based on the experimental results, this study suggests that the larger stud diameter and higher strength concrete promoted the shear capacity and stiffness but with the losing of ductility. The addition of steel fiber in pocket concrete would promote the ductility effectively, but without apparent improvement of bearing capacity or even declining the initial stiffness of specimens. It can also be confirmed that the precast steel-concrete composite structure can be adopted in practice engineering, with an acceptable ductility (6.74 mm) and minor decline of stiffness (4.93%) and shear capacity (0.98%). Due to the inapplicability of current design provision, a more accurate model was proposed, which can be used for predicting the interface shear capacity well for specimens with wide ranges of the stud diameters (from13 mm to 30 mm) and the concrete strength (from 26 MPa to 200 MPa).

• Ocean and Polar Research
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• v.28 no.3
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• pp.225-236
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• 2006

Seagrass meadows are considered as critical habitats for a wide variety of marine organisms in coastal and estuarine ecosystems. In many cases, studies on the spatial/temporal distribution of seagrass have depended on direct observations using SCUBA diving. As an alternative method fur studying seagrass distribution, an application of hydroacoustic technique has been assessed for mapping seagrass distribution in Dongdae Bay, on the south coast of Korea, in September 2005. Data were collected using high frequency transducer (420 kHz split-beam), which was installed with towed body system. The system was linked to DGPS to make goo-referenced data. Additionally, in situ seagrass distribution has been observed using underwater cameras and SCUBA diving at four stations in order to compare with acoustic data. Acoustic survey was conducted along 23 transects with 3-4 blot ship speed. Seagrass beds were vertically limited to depths less than 3.5m and seagrass height ranged between 55 and 90cm at the study sites. Dense seagmss beds were mainly found at the entrance of the bay and at a flat area around the center of the bay. Although the study area was a relatively small, the vertical and spatial distributions of the seagrass were highly variable with bathymetry and region. Considering dominant species, Zostera marina L., preliminary estimation of seagrass biomass with acoustic and direct sampling data was approximately $56.55g/m^2$, and total biomass of 104 tones (coefficient variation: 25.77%) was estimated at the study area. Hydroacoustic method provided valuable information to understand distribution pattern and to estimate seagrass biomass.

• Journal of Digital Convergence
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• v.18 no.2
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• pp.377-383
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• 2020

Digital signage is constantly being researched as new digital video platform to replace existing signage market. Traditionally, It conveys various information combining still images with text. Nowadays, it is rapidly exchanging to multi digital platform by high specificaton system, improvement of internet speed and advancement of video and audio compression technology with HTML5 technology. Not only a single wide-screen display but also the combination and adjustment of screens with setop box, OLED, media facades, and lase beam projectors are transformed into various forms to enable creative and diverse attempts for graphic designers. This study focuses on the application of motion graphics in rapidly evolving future platform - digital signage, and looking forward to help digital video content creator, researchers, and motion graphic designers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.37-42
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• 2004

In order to monitor the impact locations in smart structures, multipoint ultrasonic sensors are to be employed. In this study, a multiplexing demodulator with wide dynamic range was proposed to detect the impact locations using FBG sensors, and a stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. Two FBG sensors were attached on the bottom side of the aluminum beam specimen and low velocity impact tests were performed to detect the one-dimensional impact locations. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely, and found the impact locations with the average location error below 0.58mm.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.1
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• pp.25-33
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• 2015

Following the previous works on the natural frequency of heaving circular cylinder, i.e. Lee and Lee (2013) and Kim and Lee (2013), an investigation of the same spirit on the 2-dimensional cylinder of Lewis form has been conducted. As before, the natural frequency is defined as that corresponding to the local maximum of the MCFR (Modulus of Complex Frequency Response), which is given by the equation of motion in the frequency domain analysis. Hydrodynamic coefficients were found by using the Ursell-Tasai method, and numerical results for them were obtained up to much higher frequencies than before, for which the method was known as numerically unstable in the past. For a wide range of H, the beam-draft ratio, and ${\sigma}$, the sectional area coefficient, including their practical ranges for a ship, results for the natural frequency were computed and presented in this work. Two approximate values for the natural frequency, one proposed by Lee (2008) and another one by the damped harmonic oscillator, were also compared with the current results, and for most cases it was observed that the current result is between the two values. Our numerical results showed that the values of the local maximum of MCFR as well as the natural frequencye increase as ${\sigma}$ increases while H decreases. At present, extension of the present finding to the 3-dimensional ship via the approximate theory like the strip method looks promising.

• Journal of Computational Design and Engineering
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• v.2 no.3
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• pp.157-164
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• 2015

This paper discusses an optimization-based approach for the design of a product platform for industrial three-axis linear-type robots, which are widely used for handling objects in manufacturing lines. Since the operational specifications of these robots, such as operation speed, working distance and orientation, weight and shape of loads, etc., will vary for different applications, robotic system vendors must provide various types of robots efficiently and effectively to meet a range of market needs. A promising step toward this goal is the concept of a product platform, in which several key elements are commonly used across a series of products, which can then be customized for individual requirements. However the design of a product platform is more complicated than that of each product, due to the need to optimize the design across many products. This paper proposes an optimization-based fundamental framework toward the design of a product platform for industrial three-axis linear-type robots; this framework allows the solution of a complicated design problem and builds an optimal design method of fundamental features of robot frames that are commonly used for a wide range of robots. In this formulation, some key performance metrics of the robot are estimated by a reducedorder model which is configured with beam theory. A multi-objective optimization problem is formulated to represent the trade-offs among key design parameters using a weighted-sum form for a single product. This formulation is integrated into a mini-max type optimization problem across a series of robots as an optimal design formulation for the product platform. Some case studies of optimal platform design for industrial three-axis linear-type robots are presented to demonstrate the applications of a genetic algorithm to such mathematical models.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.2
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• pp.117-123
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• 2004

A 30 nm $In_{0.7}GaAs$ High Electron Mobility Transistor (HEMT) with triple-gate has been successfully fabricated using the $SiO_2/SiN_x$ sidewall process and BCB planarization. The sidewall gate process was used to obtain finer lines, and the width of the initial line could be lessened to half by this process. To fill the Schottky metal effectively to a narrow gate line after applying the developed sidewall process, the sputtered tungsten (W) metal was utilized instead of conventional e-beam evaporated metal. To reduce the parasitic capacitance through dielectric layers and the gate metal resistance ($R_g$), the etchedback BCB with a low dielectric constant was used as the supporting layer of a wide gate head, which also offered extremely low Rg of 1.7 Ohm for a total gate width ($W_g$) of 2x100m. The fabricated 30nm $In_{0.7}GaAs$ HEMTs showed $V_{th}$of -0.4V, $G_{m,max}$ of 1.7S/mm, and $f_T$ of 421GHz. These results indicate that InGaAs nano-HEMT with excellent device performance could be successfully fabricated through a reproducible and damage-free sidewall process without the aid of state-of-the-art lithography equipment. We also believe that the developed process will be directly applicable to the fabrication of deep sub-50nm InGaAs HEMTs if the initial line length can be reduced to below 50nm order.

• Journal of the Korean earth science society
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• v.26 no.8
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• pp.836-843
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• 2005

Two data sets of repeated hydrographic surveys with a single beam echo-sounder were obtained to investigate morphological changes on a sand mining site within EEZ near the Eocheong Islands, West Sea of Korea. Their accuracies of depth measurement, estimated from the crossover analysis, correspond to the Oder 2 of IHO standards. Bathymetric maps show a feature of 300m wide and 10m deep hollow, whose evolution can be seen in difference grids of the two bathymetric maps. However, data of higher accuracy and resolution enable precise quantification of extracted sand volume. Since this morphological change could affect sedimentary environment as well as benthic ecology, environmental impact assessment based on scientific research data is required for management and sustainable development of limited sand resource.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.6
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• pp.559-566
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• 2017

This paper proposes a new composite deckplate system reinforced with inverted triangular truss girders(called 'D Deck'), which does not require the use of temporary supports at construction stage. The proposed system retains increased stiffness and strength while keeping the absolute floor height change to a minimum level and can be utilized as floor systems of various types beam members such as the conventional wide-flange and U-shaped composite beams. In order to evaluate the performance of the proposed system, five specimens with a span of 5.5 m were fabricated and tested under field loading conditions consisting of several intermediate steps. The load-deflection curves of each specimen were plotted and compared with the nonlinear three-dimensional finite element analysis results. The comparison showed that the effective load sharing between the truss girders and floor deck occurs and the maximum deflection under construction stage loading is well below the limit estimated by the provisions in Korea Building Code.

• Steel and Composite Structures
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• v.27 no.6
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• pp.727-745
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• 2018

The design criteria and the corresponding performance levels characterize the response of extended stiffened end-plate beam-to-column joints. In order to guarantee a ductile behavior, hierarchy criteria should be adopted to enforce the plastic deformations in the ductile components of the joint. However, the effectiveness of thesecriteria can be impaired if the actual resistance of the end-plate material largely differs from the design value due to the potential activation of brittle failure modes of the bolt rows (e.g., occurrence of failure mode 3 in the place of mode 1 per bolt row). Also the number and the position of bolt rows directly affect the joint response. The presence of a bolt row in the center of the connection does not improve the strength of the joint under both gravity, wind and seismic loading, but it can modify the damage pattern of ductile connections, reducing the gap opening between the end-plate and the column face. On the other hand, the presence of a central bolt row can influence the capacity of the joint to resist the catenary actions developing under a column loss scenario, thus improving the joint robustness. Aiming at investigating the influence of these features on both the cyclic behavior and the response under column loss, a wide range of finite element analyses (FEAs) were performed and the main results are described and discussed in this paper.