• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.34 no.3
• /
• pp.151-157
• /
• 2021

This paper is devoted to a convergence study of the nonlocal integral operator in peridynamics. The implicit formulation can be an efficient approach to obtain the static/quasi-static solution of crack propagation problems. Implicit methods require constly large-matrix operations. Therefore, convergence is important for improving computational efficiency. When the radial influence function is utilized in the nonlocal integral equation, the fractional Laplacian integral equation is obtained. It has been mathematically proved that the condition number of the system matrix is affected by the order of the radial influence function and nonlocal horizon size. We formulate the static crack problem with peridynamics and utilize Newton-Raphson methods with a preconditioned conjugate gradient scheme to solve this nonlinear stationary system. The convergence behavior and the computational time for solving the implicit algebraic system have been studied with respect to the order of the radial influence function and nonlocal horizon size.

• Structural Engineering and Mechanics
• /
• v.78 no.5
• /
• pp.599-610
• /
• 2021

Early detection of small concrete crack or reinforcement corrosion is necessary for Structural Health Monitoring (SHM). Global vibration based methods are advantageous over local methods because of simple equipment installation and cost efficiency. Among vibration based techniques, FRF based methods are preferred over modal based methods. In this study, a new coupled method using frequency response function (FRF) and proper orthogonal modes (POM) is proposed by using the dynamic characteristic of a damaged beam. For the numerical simulation, wave finite element (WFE), coupled with traditional finite element (FE) method is used for effectively incorporating the damage related information and faster computation. As reported in literature, hybrid combination of wave function based wave finite element method and shape function based finite element method can addresses the mid frequency modelling difficulty as it utilises the advantages of both the methods. It also reduces the dynamic matrix dimension. The algorithms are implemented on a three-dimensional reinforced concrete beam. Damage is modelled and studied for two scenarios, i.e., crack in concrete and rebar corrosion. Single and multiple damage locations with different damage length are also considered. The proposed methodology is found to be very sensitive to both single- and multiple- damage while being computationally efficient at the same time. It is observed that the detection of damage due to corrosion is more challenging than that of concrete crack. The similarity index obtained from the damage parameters shows that it can be a very effective indicator for appropriately indicating initiation of damage in concrete structure in the form of spread corrosion or invisible crack.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.18 no.3
• /
• pp.7-18
• /
• 2022

Secondary batteries used in electric vehicles have a potential risk of ignition and explosion. Various safety measures are being taken to prevent these risks. A numerical study was performed using a computational fluid dynamics code on the cases where pressure relief vents that can reduce the blast overpressures of batteries were installed in the through-compression test room, short-circuit drop test room, combustion test room, and immersion test room in facilities rleated to battery used in electric vehicles. This study was conducted using the weight of TNT equivalent to the energy release from the battery, where the the thermal runaway energy was set to 324,000 kJ for the capacity of the lithium-ion battery was 90 kWh and the state of charge (SOC) of the battery of 100%. The explosion energy of TNT (△H_TNT) generally has a range of 4,437 to 4,765 kJ/kg, and a value of 4,500 kJ/kg was thus used in this study. The dimensionless explosion efficiency coefficient was defined as 15% assuming the most unfavorable condition, and the TNT equivalent mass was calculated to be 11 kg. The internal explosion generated in a test room shows the very complex propagation behavior of blast waves. The shock wave generated after the explosion creates reflected shock waves on all inner surfaces. If the internally reflected shock waves are not effectively released to the outside, the overpressures inside are increased or maintained due to the continuous reflection and superposition from the inside for a long time. Blast simulations for internal explosion targeting four test rooms with pressure relief vents installed were herein conducted. It was found that that the maximum blast overpressure of 34.69 bar occurred on the rear wall of the immersion test room, and the smallest blast overpressure was calculated to be 3.58 bar on the side wall of the short-circuit drop test room.

• Advances in concrete construction
• /
• v.13 no.1
• /
• pp.83-99
• /
• 2022

The two, NBD and SCB tests using gypsum circular discs each containing a single notch have been experimentally accomplished in a rock mechanics laboratory. These specimens have also been numerically modelled by a two-dimensional particle flow which is based on Discrete Element Method (DEM). Each testing specimen had a thickness of 5 cm with 10 cm in diameter. The specimens' lengths varied as 2, 3, and 4 cm; and the specimens' notch angles varied as 0°, 45° and 90°. Similar semi-circular gypsum specimens were also prepared each contained one edge notch with angles 0° or 45°. The uniaxial testing machine was used to perform the experimental tests for both NBD and SCB gypsum specimens. At the same time, the numerical simulation of these tests were performed by PFC2D. The experimental results showed that the failure mechanism of rocks is mainly affected by the orientations of joints with respect to the loading directions. The failure mechanism and fracturing patterns of the gypsum specimens are directly related to the final failure loading. It has been shown that the number of induced tensile cracks showing the specimens' tensile behavior, and increases by decreasing the length and angle of joints. It should be noted that the fracture toughness of rocks' specimens obtained by NBD tests was higher than that of the SCB tests. The fracture toughness of rocks usually increases with the increasing of joints' angles but increasing the joints' lengths do not change the fracture toughness. The numerical solutions and the experimental results for both NDB and SCB tests give nearly similar fracture patterns during the loading process.

• Korean Journal of Optics and Photonics
• /
• v.32 no.4
• /
• pp.180-186
• /
• 2021

Fluorinated polyimide has excellent light transmittance and a high optical refractive index, and is useful for producing optical-waveguide phase modulators with low optical loss and low electric power consumption. In this work, an optical-waveguide phase modulator is designed and fabricated based on a high-refractive-index fluorinated polyimide, and its characteristics are measured. An efficient protocol for characterizing the loss components of the optical waveguide is proposed, and the propagation loss of the fabricated polyimide optical waveguide is confirmed to be 0.9 dB/cm. The phase modulator requires 9.1 mW of power for phase change of π, and the response time is 290 μs, which is improved by tenfold compared to a previous demonstration of polymeric phase modulators.

• KEPCO Journal on Electric Power and Energy
• /
• v.8 no.1
• /
• pp.5-7
• /
• 2022

KEPCO's plan is undergoing a trial operation to replace the open-loop section with ring main units configuration where underground distribution lines are installed, by linking the multi-way circuit breakers auto (MCA) on the power side of each pad-mounted transformer. However, ring main units application mentioned above may cause the ripple effects, when implementing the configuration without a study of protection coordination. Because ring main units with classical pre-set protection devices contribution in fault condition didn't consider yet. For the reliable ring main units operation, it is necessary to resolve several protection issues such as the protection coordination with substation side, prevention of the transformer inrush current. These issues can radically deteriorate the distribution system reliability Hence, it is essential to design proper protection coordination to reduce these types of problems. This paper presents a scheme of ring main units' configuration and MCA's settings of time-current curves to preserve the performance of protection coordination among the switchgears considering constraints, e.g. prevention of the ripple effects (on the branch section when a transformer failure occurs and the mainline when a branch line failure occurs). It was confirmed that the propagation of the failure for each interrupter segment could be minimized by applying the proposed TCC and the interrupter settings for the MCAs (branch, transformer). Further, it was verified that the undetected area of the distribution automation system (DAS) could be supplemented by having the MCA configurated ring main units operate first, instead of the internal protection equipment in the transformer such as the fuse, STP when a transformer failure occurs.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.17 no.2
• /
• pp.145-156
• /
• 2021

Ultrasonic Nanocrystal Surface Modification (UNSM) is a peening technology that generates elastic-plastic deformation on the material surface to which a static load of a air compressor and a dynamic load of ultrasonic vibration energy are applied by striking the material surface with a strike pin. In the UNSM-treated material, the structure of the surface layer is modified into a nano-crystal structure and compressive residual stress occurs. When UNSM is applied to welds in a reactor coolant system where PWSCC can occur, it has the effect of relieving tensile residual stress in the weld and thus suppressing crack initiation and propagation. In order to quantitatively evaluate the compressive residual stress generated by UNSM, many finite element studies have been conducted. In existing studies, single-path UNSM or UNSM in a limited area has been simulated due to excessive computing time and analysis convergence problems. However, it is difficult to accurately calculate the compressive residual stress generated by the actual UNSM under these limited conditions. Therefore, in this study, a minimum finite element peening analysis area that can reliably calculate the compressive residual stress is proposed. To confirm the validity of the proposed analysis area, the compressive residual stress obtained from the experiment are compared with finite element analysis results.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.18 no.2
• /
• pp.291-298
• /
• 2023

SRAM-based in-memory computing is one of the technologies to solve the bottleneck of von Neumann architecture. In order to achieve SRAM-based in-memory computing, it is essential to design efficient SRAM bit-cell. In this paper, we propose a low-power differential sensing 8+T SRAM bit-cell which reduces power consumption and improves circuit performance. The proposed 8+T SRAM bit-cell is applied to ripple carry adder which performs SRAM read and bitwise operations simultaneously and executes each logic operation in parallel. Compared to the previous work, the designed 8+T SRAM-based ripple carry adder is reduced power consumption by 11.53%, but increased propagation delay time by 6.36%. Also, this adder is reduced power-delay-product (PDP) by 5.90% and increased energy-delay- product (EDP) by 0.08%. The proposed circuit was designed using TSMC 65nm CMOS process, and its feasibility was verified through SPECTRE simulation.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.2
• /
• pp.5-17
• /
• 2007

Various field setup and filtering criteria have been suggested to avoid the near field effects in surface wave methods. Unlike other surface wave methods HWAW method uses the near field component positively. It is possible by using maximum energy point based on time-frequency map and inversion method to consider receiver locations from the source point and body wave component. To verify the HWAW method in the near field numerical study was performed and the wave propagation in the stratified soil media was simulated due to a surface point load. All of five representative soil models were used. The experimental dispersion curves, determined by HWAW method at the various receiver distances in the region of near field, all coincided well with the theoretical dispersion curves determined by 3D forward modeling (Kausel's method). Consequently, it was considered that the HWAW method can provide reliable $V_s$ profiles effectively in the near field.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.1
• /
• pp.51-65
• /
• 2007

The purpose of this study is the development and application of a high resolution ultrasonic wave imaging system to detect discontinuity plane in lab-scale rock models. This technique is based on received time series which capture the multiple reflections at interface. This study includes the fundamental aspects of ultrasonic wave propagation in rock mass, the selection of the optimal ultrasonic wave transducer, data gathering, a signal processing, imaging methods, and experiments. Experiments are carried out by the horizontal movement and rotation devices. Experimental studies show the discontinuity is well detected by the horizontal movement and rotation devices under water. Furthermore, the discontinuity and the cavity on the plaster block are identified by the rotation device. This study suggests that the new method may be an economical and effective tool for the detection of the discontinuity on rock mass.