• Journal of the Korean Society for Precision Engineering
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• v.27 no.10
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• pp.29-33
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• 2010

UV laser micromachining of metallic materials has been used in microelectronic and other industries. This paper shows on experimental investigation of micromachining of copper using a 355nm UV laser with 50ns pulse duration. A finite element model with high strain rate effect is especially suggested to investigate the phenomena which are only dominated by mechanically pressure impact in disregard of thermally heat transfer. In order to consider the strain rate effect, Cowper-Symonds model was used. To analyze the dynamic deformation during a very short processing time, which is nearly about several tens nanoseconds, a commercial Finite Element Analysis (FEA) code, LS-DYNA 3D, was employed for the computational simulation of the UV laser micro machining behavior for thin copper material. From these computational results, depth of the dent (from one to six pulsed) were observed and compared with previous experimental results. This will help us to understand interaction between UV laser beam and material.

• Geomechanics and Engineering
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• v.35 no.4
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• pp.449-464
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• 2023

Advanced nonlinear effective stress constitutive models are started to be frequently used in one-dimensional (1D) and two-dimensional (2D) site response analysis for assessment of porewater generation and liquefaction potential in soft soil deposits. The emphasis of this research is on the assessment of the implementation of this category of models at the element stage. Initially, the performance of a coupled porewater pressure (PWP) and constitutive models were evaluated employing a catalogue of 40 unidirectional cyclic simple shear tests with a variety of relative densities between 35% and 80% and effective vertical stresses between 40 and 80 kPa. The authors evaluated three coupled constitutive models (PDMY02, PM4SAND and PDMY03) using cyclic direct simple shear tests and for decide input parameters used in the model, procedures are recommended. The ability of the coupled model to capture dilation as strength is valuable because the studied models reasonably capture the cyclic performance noted in the experiments and should be utilized to conduct effective stress-based 1D and 2D site response analysis. Sandy soils may become softer and liquefy during earthquakes as a result of pore-water pressure (PWP) development, which may have an impact on seismic design and site response. The tested constitutive models are mathematically coupled with a cyclic strain-based PWP generation model and can capture small-strain stiffness and large-strain shear strength. Results show that there are minor discrepancies between measured and computed excess PWP ratios, indicating that the tested constitutive models provide reasonable estimations of PWP increase during cyclic shear (r_u) and the banana shape is reproduced in a proper way indicating that dilation and shear- strain behavior is well captured by the models.

• Journal of Auto-vehicle Safety Association
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• v.10 no.2
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• pp.6-12
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• 2018

Optimized section shape of aluminum bumper backbeam for enhancing the front high speed crashworthiness was investigated. Front body analysis model of a convertible vehicle was built up and parameter studies were carried out with changing the inner rib shape and the section thickness distribution. First an inner rib shape displaying most efficient structural performance was selected. Next, for the selected section the effect of section thickness combination was examined. Also, a light weighed backbeam section displaying crash performance over the current design was suggested. Finally RCAR front low speed impact analyses were carried out for the optimized models.

• Structural Engineering and Mechanics
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• v.3 no.5
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• pp.463-474
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• 1995

When a tubular cantilever beam is loaded by a dynamic force applied transversely at its tip, the strain hardening of the material tends to increase the load carrying capacity and local buckling and cross-sectional overlization occurring in the tube section tends to reduce the moment carrying capacity and results in structural softening. A theoretical model is presented in this paper to analyze the deformation of a tubular beam in a dynamic response mode. Based on a large deflection analysis, the hardening/softening M-${\kappa}$ relationship is introduced. The main interest is on the curvature development history and the deformed configuration of the beam.

• Advances in nano research
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• v.14 no.3
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• pp.247-259
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• 2023

Muscle strength and hypertrophy are equivalent when low-intensity resistance exercise is paired with blood flow restriction. This paper deals with the impact of physical exercise in the form of body activities on drug delivery using nanodevices. The body's actions impact the blood flow since the nano drug delivery devices are released into the bloodstream, and physical exercise and all the activities that change the blood flow influence the stability of these nanodevices. The nanodevice for the drug delivery purpose is modeled via nonuniform tube structures based on the high-order beam theory along with the nonlocal strain gradient theory. The nanodevice is made by a central nanomotor as well as two nanoblade in the form of truncated conical nanotubes carrying the nanomedicine. The mathematical simulation of rotating nanodevices is numerically solved, and the effect of various parameters on the stability of nanodevices has been studied in detail after the validation study.

• International Journal of Internet, Broadcasting and Communication
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• v.16 no.3
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• pp.77-84
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• 2024

Aberration is still a problem for making augmented reality displays. The existing methods to solve this problem are either slow and inefficient, consume too much battery, or are too complex for straightforward implementation. There are still some problems with image quality, and users may suffer from eye strain and headaches because the images provided to each eye lack accuracy, causing the brain to receive mismatched cues between the vergence and accommodation of the eyes. In this paper, we implemented a computer simulation of an optical aberration using Zernike polynomials which are defocus, trefoil, coma, and spherical. The research showed that these optical aberrations impact the Point Spread Function (PSF) and Modulation Transfer Function (MTF). We employed the phase conjugate technique to mitigate aberrations. The findings revealed that the most significant impact on the PSF and MTF comes from the influence of spherical aberration and coma aberration.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.59-78
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• 2024

In tunnel construction, the stability is evaluated by the settlement of adjacent structures and ground, but the shear strain of the ground is the main factor that determines the failure mechanism of the ground due to the tunnel excavation and the change of the operating load, and can be used to review the stability of the tunnel excavation and to calculate the reinforcement area. In this study, a twin tunnel excavation was simulated on a soft ground in an urban area through a laboratory model test to analyze the behavior of the twin tunnel excavation on the adjacent pile grouped foundation and adjacent ground. Both the displacement and the shear strain of ground were obtained using a close-range photogrammetry during laboratory model test. In addition, two-dimensional finite element numerical analysis was performed based on the model test. The results of a back-analysis showed that the maximum shear strain rate tends to decrease as the horizontal distance between the pillars of the twin tunnel and the vertical distance between the toe of the pile group and the crown of the tunnel were decreased. The impact of the second tunnel on the first tunnel and pile group was decreased as the horizontal distance between the pillars of the twin tunnel was increased. In addition, the vertical distance between the toe of the pile group and the crown of the tunnel had a relatively greater impact on the shear strain results than the horizontal distance of the pillars between the twin tunnels. According to the results of the close-range photogrammetry and numerical analysis, the settlement of adjacent pile group and adjacent ground was measured within the design criteria, but the shear strain of the ground was judged to be outside the range of small strain in all cases and required reinforcement.

• Structural Engineering and Mechanics
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• v.53 no.1
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• pp.73-87
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• 2015

In case of aircraft impact on nuclear containment structures, the initial kinetic energy of the aircraft is transferred and absorbed by the outer containment, may causing either complete or partial failure of containment structure. In the present study safety analysis of BWR Mark III type containment has been performed. The total height of containment is 67 m. It has a circular wall with monolithic dome of 21m diameter. Crash analysis has been performed for fighter jet Phantom F4. A normal hit at the crown of containment dome has been considered. Numerical simulations have been carried out using finite element code ABAQUS/Explicit. Concrete Damage Plasticity model have been incorporated to simulate the behaviour of concrete at high strain rate, while Johnson-Cook elasto-visco model of ductile metals have been used for steel reinforcement. Maximum deformation in the containment building has reported as 33.35 mm against crash of Phantom F4. Deformations in concrete and reinforcements have been localised to the impact region. Moreover, no significant global damage has been observed in structure. It may be concluded from the present study that at higher velocity of aircraft perforation of the structure may happen.

• Journal of the Korea Safety Management & Science
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• v.19 no.1
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• pp.245-255
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• 2017

This paper is a study to estimate the noise generated by fluid around each machine in the basement and basement facilities that accept major noise factor, pump fluid mechanical equipment installed to evaluate the impact on the real working environment. In particular, the review of the reliability of complementary information and reliability predict the natural frequency for generating a maximum strain when the vibration analysis, and intended to ensure that the design to avoid a natural frequency of the structure, on the basis of the this analysis result to the subject a real building.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.111-116
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• 2018

This research examines the drop impact of an external cooling unit package of an air conditioner system. The packaging is composed of a shock-absorbing material, which protects the package contents by absorbing the impact energy and other parts for fixture. Accurate quantification of the impact acceleration experienced by the package contents is necessary to design an effective packaging with minimal volume and sufficient shock absorbing capacity. Explicit time integration was used for the drop impact analyses. A finite element model of the package was constructed, material testing and material model selection were carried out, and sensors for data acquisition were modeled to obtain accurate simulation results. The results were compared with real physical test data. Due to imprecise modeling of the damping, the acceleration and strain values predicted by the simulation were larger than those from physical test. However, the trend of the history data and the peak deceleration value in the direction of impact showed good agreements. Thus, the analysis model and scheme are suitable for the design of an air conditioner cooling unit package.