• Structural Engineering and Mechanics
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• v.74 no.1
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• pp.1-18
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• 2020

For the large deformation of shear walls under vertical and horizontal loads, there are difficulties in obtaining accurate simulation results using the response analysis method, even with fine mesh elements. Furthermore, concrete material nonlinearity, stiffness degradation, concrete cracking and crushing, and steel bar damage may occur during the large deformation of reinforced concrete (RC) shear walls. Matrix operations that are involved in nonlinear analysis using the traditional finite-element method (FEM) may also result in flaws, and may thus lead to serious errors. To solve these problems, a planar four-node element was developed based on vector mechanics. Owing to particle-based formulation along the path element, the method does not require repeated constructions of a global stiffness matrix for the nonlinear behavior of the structure. The nonlinear concrete constitutive model and bilinear steel material model are integrated with the developed element, to ensure that large deformation and damage behavior can be addressed. For verification, simulation analyses were performed to obtain experimental results on an RC shear wall subjected to a monotonically increasing lateral load with a constant vertical load. To appropriately evaluate the parameters, investigations were conducted on the loading speed, meshing dimension, and the damping factor, because vector mechanics is based on the equation of motion. The static problem was then verified to obtain a stable solution by employing a balanced equation of motion. Using the parameters obtained, the simulated pushover response, including the bearing capacity, deformation ability, curvature development, and energy dissipation, were found to be in accordance with the experimental observation. This study demonstrated the potential of the developed planar element for simulating the entire process of large deformation and damage behavior in RC shear walls.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2022.05a
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• pp.494-497
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• 2022

Recently, the damage caused by flash floods caused by extreme weather due to global warming is increasing. In order to reduce the damage, this paper conducted a study on the search for the shortest route of an evacuation route due to a flash flood. For this, we implemented a route search system using GIS and shape files including buildings and roads and Dijkstra's algorithm. In this study, the location of users close to the point where the flash flood occurs is identified, and the evacuation route is searched from the starting point to the destination point without passing through the dangerous point. Evacuate out of the test bed, or designate a building in the test bed as an evacuation shelter, and search for a route to the nearest evacuation shelter. Accordingly, it is expected that human damage will be reduced by providing the shortest evacuation route.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.2
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• pp.109-120
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• 2017

A discounted cost model for preventive maintenance of armor units of rubble-mound breakwaters is mathematically derived by combining the deterioration model based on a discrete-time stochastic process of shock occurrence with the cost model of renewal process together. The discounted cost model of condition-based maintenance proposed in this paper can take into account the nonlinearity of cumulative damage process as well as the discounting effect of cost. By comparing the present results with the previous other results, the verification is carried out satisfactorily. In addition, it is known from the sensitivity analysis on variables related to the model that the more often preventive maintenance should be implemented, the more crucial the level of importance of system is. However, the tendency is shown in reverse as the interest rate is increased. Meanwhile, the present model has been applied to the armor units of rubble-mound breakwaters. The parameters of damage intensity function have been estimated through the time-dependent prediction of the expected cumulative damage level obtained from the sample path method. In particular, it is confirmed that the shock occurrences can be considered to be a discrete-time stochastic process by investigating the effects of uncertainty of the shock occurrences on the expected cumulative damage level with homogeneous Poisson process and doubly stochastic Poisson process that are the continuous-time stochastic processes. It can be also seen that the stochastic process of cumulative damage would depend directly on the design conditions, thus the preventive maintenance would be varied due to those. Finally, the optimal periods and scale for the preventive maintenance of armor units of rubble-mound breakwaters can be quantitatively determined with the failure limits, the levels of importance of structure, and the interest rates.

• Computers and Concrete
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• v.12 no.3
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• pp.351-375
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• 2013

Post-punching resistance of a flat slab can help redistribute the gravity loads and resist progressive collapse of a structure following initial damage. One important difficulty with accounting for the post-punching strength of a slab is the discontinuity that develops following punching shear. A numerical simulation technique is proposed here to model and evaluate post-punching resistance of flat slabs. It is demonstrated that the simulation results of punching shear and post-punching response of the model of a slab on a single column are in good agreement with corresponding experimental data. It is also shown that progressive collapse due to a column removal (explosion) can lead to punching failure over an adjacent column. Such failure can propagate throughout the structure leading to the progressive collapse of the structure. Through post-punching modeling of the slab and accounting for the associated discontinuity, it is also demonstrated that the presence of an adequate amount of integrity reinforcement can provide an alternative load path and help resist progressive collapse.

• Annual Conference of KIPS
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• 2006.05a
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• pp.1117-1120
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• 2006

Wide applications because of their flexibilities and conveniences of Wireless Mobile Ad-hoc Networks (MANETs) also make them more interesting to adversaries. Currently, there is no applied architecture efficient enough to protect them against many types of attacks. Some preventive mechanisms are deployed to protect MANETs but they are not enough. Thus, MANETs need an Intrusion Detection System (IDS) as the second layer to detect intrusion of adversaries to response and diminish the damage. In this paper, we propose an algorithm for detecting bogus nodes when they attempt to intrude into network by attack routing protocol. In addition, we propose a procedure to find the most optimize path between two nodes when they want to communicate with each other. We also show that our algorithm is very easy to implement in current proposed architectures.

• The KSFM Journal of Fluid Machinery
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• v.2 no.3 s.4
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• pp.24-29
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• 1999

The ASME strainers have been newly installed at the suction side of each reactor coolant pump to get rid of the foreign materials which may damage the pump impeller or interfere with the coolant path of fuel flow tube or primary plate type heat exchanger. The strainer was designed in accordance with ASME SEC. III, DIV. 1, Class 3 and the structural integrity was verified by seismic analysis. The screen was designed in accordance with the effective void area from the result of flow analysis for T-type strainer. After installation of the strainer, it was confirmed through the field test that the flow characteristics of primary cooling system were not adversely affected. The pressure loss coefficient was calculated by Darcy equation using the pressure difference through each strainer and the flow rate measured during the strainer performance test. And these are useful data to predict flow variations by the pressure difference.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.4
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• pp.69-80
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• 2000

Generally, die polishing is a lime consuming process, resulting in 30∼50％ of the whole die manufacturing time. However, die polishing has not been automated yet, since it needs a great deal of experience and skill. This paper describes a new development of automated system for die polishing and focuses on the successful achievements of the element techniques to realize from hand skill to automation, as followings: (1) The 5 axes polishing system by the aid of robot with 2 degrees of freedom, is developed for the application of curved surface die. (2) The CAM system realizes a 5 axes tool path control for polishing and measuring. (3) The conductive elastic tool is able to meet curved surfaces of die and gives a high efficient and quality polishing characteristics. (4) The surface roughness measurement device with noncontact laser is developed and has a high reliability without surface damage.

• Geomechanics and Engineering
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• v.11 no.3
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• pp.373-383
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• 2016

As one natural material, the physical and mechanical properties of rock will be affected very largely by chemical erosion environment. Under chemical environment, the strength of rock will be reduced. Considering the effect of the chemical erosion, fracture factor of rock is reduced. The damage variable is applied to express the change of fracture stress. Therefore, the fracture criterion of rock under chemical environment is constructed. By one experiment of rock fracture under chemical erosion environment, the proposed fracture criterion is verified. The results show that, the fracture path by theory is agree with the testing one well.

• Journal of the Korean Society of Safety
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• v.33 no.3
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• pp.8-14
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• 2018

Ni-base superalloy has excellent resistance to extreme environments such as high temperatures and high stresses and are used as materials for large gas turbines. In this paper, the specimens were taken from the blade that were used for a long time, and their life span was studied by microstructure analysis and avoidance of cursing. The microstructural analysis of the specimens was carried out using a OM and SEM to observe the coarsening, carbides on gamma prime. Low-cycle fatigue tests were performed on new material and airfoil of long time-used blade. The test was conducted under various deformation conditions and temperature conditions of $760^{\circ}C$ and $870^{\circ}C$. The low cycle fatigue test was carried out using the Coffin-Manson equation and the fatigue life was predicted. After the test, crack path and fracture surface were analyzed using SEM.

• Journal of Korea Multimedia Society
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• v.19 no.3
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• pp.539-547
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• 2016

Automated guided vehicles (AGVs) are widely used in industry. Several types of vision-based AGVs have been studied in order to reduce cost of infrastructure building at floor of workspace and to increase flexibility of changing the navigation path layout. A practical vision-based guideline tracing method is proposed in this paper. A virtual tracing wheel is introduced and adopted in this method, which enables a vision-based AGV to trace a guideline in diverse ways. This method is also useful for preventing damage of the guideline by enforcing the real steering wheel of the AGV not to move on the guideline. Usefulness of the virtual tracing wheel is analyzed through computer simulations. Several navigation tests with a commercial AGV were also performed on a usual guideline layout and we confirmed that the virtual tracing wheel based tracing method could work practically well.