• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.7
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• pp.927-935
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• 2019

Screw-failure accidents in small ships frequently occur in coastal waters. In particular, vessels' propulsion systems are frequently coiled due to objects such as fish-nets and ropes that float on the sea. The failure of the ship's propulsion system can cause primary accidents such as ship operation delays and drifting due to loss of power; furthermore, the possibility of secondary accidents such as those involving operators in the underwater removal of rope stuck in a propeller. Ships that do not have the proper tools to solve these problems must be either lifted onto land to be repaired or divers must dive directly under the ship to solve the problem. Accordingly, some small vessels have been equipped with rope-cutter devices on the propeller shaft to prevent ship propeller system accidents in recent years; however, they are not being applied efficiently due to the cost and time of installation. To solve these problems, this study develops an underwater rope-cutter device and controller for the removal of propeller and shaft foreign material in small vessels. This device has simple structures that use the principle of a saw. Meteor gears and crank pins were used for the straight-line rotation of saw blades of the underwater rope-cutters to allow for long strokes. Furthermore, the underwater rope-cutting machines can be operated by being connected to the ship battery. The user, a non-professional, can ensure convenience and stability by applying reverse current prevention and a speed control circuit so that it can be used more conveniently and safely.

• Economic and Environmental Geology
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• v.41 no.4
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• pp.383-392
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• 2008

This study aims to evaluate the mechanical-chemical stability of used coal ash blocks, for improving fishing grounds. The surface of weathered ash blocks in seawater showed a decrease in the Ca and an increase in the Mg contents, compared to that of fresh blocks. This result reflects the substitution of Ca by Mg in seawater. The compressive strengths of ash blocks submerged into seawater during 12 months ranged from 235.23 to $447.43\;kgf/cm^2$; this is higher than the standard strength of wave-absorbing blocks($180\;kgf/cm^2)$ that are used for harbor construction. In addition, the compressive strength of ash blocks tends to increase with increasing installation time in seawater. The result of leaching experiments on coal ash blocks by Korean Standard Leaching Test(KSLT) method showed that leached concentrations of most metals except Cr(that leached up to 50 ppb, approaching standard concentration) do not exceed the seawater quality standards. A long-term(112 days) heavy metal leaching test to analyze seawater without mixing-dilution also showed that the concentrations of leached heavy metals, except for Cu, under anaerobic conditions do not exceed the seawater quality standards. Accordingly, the use of coal ash blocks in marine environments appears to be safe from chemical and mechanical factors that decrease the efficiency of concrete. Also, leaching concentration of Cu seems to be stable by decrease of leaching concentration due to dilution of seawater.

• Structural Engineering and Mechanics
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• v.72 no.1
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• pp.99-111
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• 2019

To investigate the seismic performance of long-span partially earth-anchored cable-stayed bridge, a super long-span partially earth-anchored cable-stayed bridge scheme with main span of 1400m is taken as example, structural response of the bridge under E1 seismic action is investigated numerically by the multimode seismic response spectrum and time-history analysis, seismic behavior and also the effect of structural geometric nonlinearity on the seismic responses of super long-span partially earth-anchored cable-stayed bridges are revealed. The seismic responses are also compared to those of a fully self-anchored cable-stayed bridge with the same main span. The effects of structural parameters including the earth-anchored girder length, the girder width, the girder depth, the tower height to span ratio, the inclination of earth-anchored cables, the installation of auxiliary piers in the side spans and the connection between tower and girder on the seismic responses of partially ground-anchored cable-stayed bridges are investigated, and their reasonable values are also discussed in combination with static performance and structural stability. The results show that the horizontal seismic excitation produces significant seismic responses of the girder and tower, the seismic responses of the towers are greater than those of the girder, and thus the tower becomes the key structural member of seismic design, and more attentions should be paid to seismic design of these sections including the tower bottom, the tower and girder at the junction of tower and girder, the girder at the auxiliary piers in side spans; structural geometric nonlinearity has significant influence on the seismic responses of the bridge, and thus the nonlinear time history analysis is proposed to predict the seismic responses of super long-span partially earth-anchored cable-stayed bridges; as compared to the fully self-anchored cable-stayed bridge with the same main span, several stay cables in the side spans are changed to be earth-anchored, structural stiffness and natural frequency are both increased, the seismic responses of the towers and the longitudinal displacement of the girder are significantly reduced, structural seismic performance is improved, and therefore the partially earth-anchored cable-stayed bridge provides an ideal structural solution for super long-span cable-stayed bridges with kilometer-scale main span; under the case that the ratio of earth-anchored girder length to span is about 0.3, the wider and higher girder is employed, the tower height-to-span ratio is about 0.2, the larger inclination is set for the earth-anchored cables, 1 to 2 auxiliary piers are installed in each of the side spans and the fully floating system is employed, better overall structural performance is achieved for long-span partially earth-anchored cable-stayed bridges.

• Journal of the Korean Solar Energy Society
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• v.39 no.1
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• pp.59-66
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• 2019

BIPV or BAPV installation applied to building is increasing through public utility mandates enterprise. Solar PV energy generates only during the day, but if it is operated in convergence with ESS, which stores electrical energy, it can restrain the fossil energy used in buildings throughout the day. A solution is to converge with PV system and ESS. However, PV systems and ESS connected to the power grid in parallel can cause problems of electrical stability. A study was conducted on the case of failure to detect islanding operation under the parallel operation of PV generation and ESS that are connected in parallel to power grid. Experiments conducted various non-islanding detections under the operating conditions. In the experiment results, when one PCS - PV inverter or ESS inverter - was operating under the islanding condition, it stopped working within 0.5 seconds of the Korean grid standard. However, when both of PV inverter and ESS inverter were operating at the same time under the islanding situation, the anti-islanding algorithm did not operate normally and both inverters continuously supplied power to the connected RLC loads. islanding detection Algorithm developed by each inverter manufacturer has caused this phenomenon. Therefore, this paper presented a new test standard for islanding detection.

• Journal of the Korean Geosynthetics Society
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• v.20 no.2
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• pp.45-56
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• 2021

As the utilization of the underground space is activated, deep excavation of ground has been conducted for the installation of underground structures, the earth retaining wall has widely used to minimize deformation of the excavated ground. In particular, as deep excavation is actively progressing in an urban area where structures are concentrated, methods to minimize the deformation of wall have been devised to prevent damage to the structure adjacent to the wall, and one of these methods is the pre-loading method. This method is a method of suppressing the deformation of wall by actively applying a load on the strut to be installed in wall, and research on this method has been conducted recently. However, although related studies have been actively conducted, the management standard for the pre-loading of bracing has not been clearly presented until now. In addition, since the working force in the strut may increase depending on the depth of excavation or the soil condition of the backfill, the magnitude of the pre-loading that can be applied to the brace may decrease. Nevertheless, the magnitude of the pre-loading (more than 50% of the working load) proposed by the previous research results has been uniformly applied to the strut. In this study, 3D finite element analysis was performed to evaluate the application range of the pre-loading of H-beam strut according to the soil conditions of backfill. As a result of the analysis, it was found that there is a very high possibility that a problem may occur in the stability of the structure of strut due to the earth pressure and the pre-loading when the soil condition is weak and deep excavation proceeds. And it was found that the application range of the pre-loading was 5%~70% of the working load in strut.

• Journal of the Korean GEO-environmental Society
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• v.12 no.3
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• pp.55-61
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• 2011

Song-Do international city is the area developed in large-scale land reclamation. Song-Do area consists of reclamation layer, sedimentary layer(loose silt, soft clay and sand alternating) and residual layer from the ground surface. Therefore, using pile foundation is inevitable to build structures safely. In this area, driven PHC piles have been generally constructed in terms of environmental and economic conditions. As a result of analyzing 4 sites in Song-Do district 5 and 7 recently, the method of driving pile has many problems because of existence of rigid soil in sedimentary layer and installation of more than 30m piles. In this case, when installing piles by drive after pre-boring up to appropriate depth, the results of constructability analysis were very good. And in the economic efficiency, although 4% of construction cost rose, it was a very slight increase in comparison with improvement of workability. In the case of the stability, more than 70% compared to the allowable stress of piles was satisfied through the load test. As a result, when PHC piles is installed in Song-Do district, the proper construction method is that piles are located at bearing layer after boring rigid sand layer.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.3
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• pp.91-98
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• 2021

The installation and performance test of the ISOL (Isotope Separation On Line) system for the generation and separation of Rare Isotopes (RI) beams is in progress at the Rare Isotope Science Project (RISP), Institute for Basic Science (IBS). The various RI beams generated by the ISOL target/ion source go through the beam lines and separators, and only the RI beam desired by the user is selected and transmitted to the superconducting linear accelerator at the downstream of the ISOL. In the ISOL system, two separators are installed to separate a specific RI beam, and control is performed by the Experimental Physics and Industrial Control System (EPICS). In this study, an EPICS IOC (Input-Output Control) was developed to measure the magnetic field of a dipole magnet for mass separation of a multivalent (n+) RI beam in the A/Q separator, which is one of the ISOL RI beam separators. The operational stability of the A/Q separator was tested through a magnetic field measurement using a Hall probe.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.120-130
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• 2022

In this study, the applicability of the microseismic monitoring system based on the underground mine communication system has been verified by operation test in the domestic underground mine. The microseismic data consists of wavelet data and meta-data for mine safety management, and both data should be transferred, stored, analyzed and managed with proper method according to the purpose and size of each data. In order to select the optimal communication system for the microseismic monitoring system considering the underground environment as well as properties of data, various types of communication system have been tested and compared during operation test after installing the optical cable communication system, 2.4 GHz and 900 MHz wireless communication system through the underground mine tunnel and overground area of the test site. The integrated microseismic monitoring software, which was developed to secure the stability of data management and ease of use, has been updated according to findings from operation test. Through the operation test of the microseismic monitoring system including the communication system and the monitoring software, the technical basis was established corresponding to various requirements of the domestic mine for adoption of the microseismic monitoring system.

• Journal of the Korea Institute of Building Construction
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• v.22 no.5
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• pp.519-530
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• 2022

As online commerce increases, the construction of large logistics buildings worldwide is exploding. Most of these buildings have the characteristics of long span and heavy loaded and use precast concrete components, a pin joint structure, for rapid construction. However, due to construction safety and structural stability requirements, the pin joint structure has many limitations in terms of the erection of the PC member, which increases the time and cost. A structural frame connected with steel joints between precast concrete components, called a SMART frame, has been developed, which addresses these constraints and risks. However, the effect of the appllication of a SMART frame on the time aspect has not been analysed. The study is a time reduction effect analysis of a SMART frame for long span and heavy loaded logistics buildings. For this study, the authors select a case site erected using existing PC components, and compare the time reduction with the SMART frame erection simulations. Through this analysis, it was found that a time reduciton about 4 months, approximately 48% of the conventional PC installation period could be achieved. If the SMART frame is applied when carrying out future large-scale logistics building projects, it can be expected to have the effect of significantly shortening the construction period compared to the conventional method.

• Journal of the Korean Geosynthetics Society
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• v.21 no.4
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• pp.101-109
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• 2022

This study describes the results of model experiment to analyze the effect of backfill material types on the behavior of underground facility. In the model experiment, backfill materials around the existing underground facility were applied with soil (Jumunjin standard sand) and CLSM. The displacement of underground facility was analyzed for each excavation stage considering the separation distance between the excavation surface and the backfill area based on the experimental results. When soil was applied as a backfill material, the soil on the back of the excavation surface collapsed by excavation and formed an angle of repose, and the process of slope stability was repeated at each excavation stage. In addition, the displacement of underground facility began to occur in the excavation stage that the failure line of soil passes the installation location of the underground facility. When CLSM was applied as a backfill material, there was almost no horizontal and vertical displacement of the ground regardless of the separation distance from the excavation surface even when excavation proceeded to the backfill depth. Therefore, this result showed that it can have a resistance effect against the lateral earth pressure generated and the collapse of the original ground by adjacent excavation, if a backfill material with high stiffness such as CLSM is applied.