• Journal of the Korea Academia-Industrial cooperation Society
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• 제18권7호
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• pp.709-713
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• 2017

In urgent situations such as crashes, the integrity of an aircraft's fuel tank is directly related to the survivability of the crew. Thus, an external auxiliary fuel tank should be robust against bird strikes. In this study, a numerical analysis was carried out using impact analysis software to analyze the influence of bird strike on a composite container for an external auxiliary fuel tank. The structure was modeled as a shell element, and the fluid and bird were modeled by the particle method. The behavior of the internal fluid was also examined. The maximum stress, deformation, and strain of the composite container were also calculated.

• Structural Engineering and Mechanics
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• 제57권3호
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• pp.507-528
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• 2016

Reduced beam section (RBS) moment resisting connections are among the most economical and practical rigid steel connections developed in the aftermath of the 1994 Northridge and the 1995 Kobe earthquakes. Although the performance of RBS connection has been widely studied, this connection has not been subject to in the skewed conditions. In this study, the seismic performance of dogbone connection was investigated at different angles. The Commercial ABAQUS software was used to simulate the samples. The numerical results are first compared with experimental results to verify the accuracy. Nonlinear static analysis with von Mises yield criterion materials and the finite elements method were used to analyze the behavior of the samples The selected Hardening Strain of materials at cyclic loading and monotonic loading were kinematics and isotropic respectively The results show that in addition to reverse twisting of columns, change in beam angle relative to the central axis of the column has little impact on hysteresis response of samples. Any increase in the angle, leads to increased non-elastic resistance. As for Weak panel zone, with increase of the angle between the beam and the column, the initial submission will take place at a later time and at a larger rotation angle in the panel zone and this represents reduced amount of perpendicular force exerted on the column flange. In balanced and strong panel zones, with increase in the angle between the beam and the central axis of the column, the reduced beam section (RBS), reaches the failure limit faster and at a lower rotation angle. In connection of skewed beam, balanced panel zone, due to its good performance in disposition of plasticity process away from connection points and high energy absorption, is the best choice for panel zone. The ratio of maximum moment developed on the column was found to be within 0.84 to 1 plastic anchor point, which shows prevention of brittle fracture in connections.

• Safety and Health at Work
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• 제9권2호
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• pp.149-158
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• 2018

Background: Work comfort studies have been extensively conducted, especially in the underground and meteorological fields resulting in an avalanche of recommendations for their evaluation. Nevertheless, no known or universally accepted model for comprehensively assessing the thermal work condition of the underground mine environment is currently available. Current literature presents several methods and techniques, but none of these can expansively assess the underground mine environment since most methods consider only one or a few defined factors and neglect others. Some are specifically formulated for the built and meteorological climates, thus making them unsuitable to accurately assess the climatic conditions in underground development and production workings. Methods: This paper presents a series of sensitivity analyses to assess the impact of environmental parameters and metabolic rate on the thermal comfort for underground mining applications. An approach was developed in the form of a "comfort model" which applied comfort parameters to extensively assess the climatic conditions in the deep, hot, and humid underground mines. Results: Simulation analysis predicted comfort limits in the form of required sweat rate and maximum skin wettedness. Tolerable worker exposure times to minimize thermal strain due to dehydration are predicted. Conclusion: The analysis determined the optimal air velocity for thermal comfort to be 1.5 m/s. The results also identified humidity to contribute more to deviations from thermal comfort than other comfort parameters. It is expected that this new approach will significantly help in managing heat stress issues in underground mines and thus improve productivity, safety, and health.

• Earthquakes and Structures
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• 제13권6호
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• pp.519-529
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• 2017

The surrounding rocks of underground openings are natural materials and their mechanical behavior under seismic load is different from traditional man-made materials. This paper proposes a framework to comprehensively model the mechanical behavior of surrounding rocks. Firstly, the effects of seismic load on the surrounding rocks are summarized. Three mechanical effects and the mechanism, including the strengthening effect, the degradation effect, and the relaxation effect, are detailed, respectively. Then, the framework for modelling the mechanical behavior of surrounding rocks are outlined. The strain-dependent characteristics of rocks under seismic load is considered to model the strengthening effect. The damage concept under cyclic load is introduced to model the degradation effect. The quantitative relationship between the damage coefficient and the relaxation zone is established to model the relaxation effect. The major effects caused by seismic load, in this way, are all considered in the proposed framework. Afterwards, an independently developed 3D dynamic FEM analysis code is adopted to include the algorithms and models of the framework. Finally, the proposed framework is illustrated with its application to an underground opening subjected to earthquake impact. The calculation results and post-earthquake survey conclusions are seen to agree well, indicating the effectiveness of the proposed framework. Based on the numerical calculation results, post-earthquake reinforcement measures are suggested.

• Steel and Composite Structures
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• 제38권2호
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• pp.151-164
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• 2021

During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Lüder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending-flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension-compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

• Structural Engineering and Mechanics
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• 제89권1호
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• pp.1-11
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• 2024

This article introduces a novel analytical model for examining the impact of porosity on shear correction factors (SCFs) in functionally graded porous beams (FGPB). The study employs uneven and logarithmic-uneven modified porosity-dependent power-law functions, which are distributed throughout the thickness of the FGP beams. Additionally, a modified exponential-power law function is used to estimate the effective mechanical properties of functionally graded porous beams. The correction factor plays a crucial role in this analysis as it appears as a coefficient in the expression for the transverse shear stress resultant. It compensatesfor the assumption that the shear strain is uniform across the depth of the cross-section. By applying the energy equivalence principle, a general expression for static SCFs in FGPBs is derived. The resulting expression aligns with the findings obtained from Reissner's analysis, particularly when transitioning from the two-dimensional case (plate) to the one-dimensional case (beam). The article presents a convenient algebraic form of the solution and provides new case studies to demonstrate the practicality of the proposed formulation. Numerical results are also presented to illustrate the influence of porosity distribution on SCFs for different types of FGPBs. Furthermore, the article validates the numerical consistency of the mechanical property changesin FG beams without porosity and the SCF by comparing them with available results.

• Journal of the Korean Institute of Gas
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• 제26권4호
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• pp.58-63
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• 2022

With the emergence of environmental problems caused by fine dust worldwide, LNG, which is cheaper and less pollution than diesel, is attracting attention as the next generation energy of automobiles and is expanding its supply. However, it is difficult to operate smoothly due to the lack of infrastructure for LNG charging stations in Korea and the limited size of containers that can be installed according to regulations. In Korea, research and development on the contents of containers for the smooth operation of natural gas vehicles are underway, but there is a problem that the container directly receives the impact of the vehicle collision and explodes, causing a major disaster. Therefore, in this study, the safety of the container was verified by deriving the strain and stress values through ANSYS Explicit Dynamics analysis. As a result, a maximum stress of 565.37MPa occurred in the container, and it is expected that plastic deformation will occur as it exceeds the yield stress of STS304 used as a material for the container, which is beyond 505MPa. When an impact caused by a collision between a vehicle and a container is applied, it is considered necessary to design a support or reinforcement because the container may be damaged or defective.

• Journal of Navigation and Port Research
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• 제39권3호
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• pp.179-184
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• 2015

The purpose of this study is to provide appropriate methodology to ensure the safety and integrity of the production riser in offshore structure. In order to select integrity estimation methodology for production riser, level I and II Non-destructive Damage Evaluation (NDE) methods that were applied to existing structures are classified and reviewed. Numerical analysis is performed to verify the applicability and capability on damage detection of reviewed methods. As a result, the damage detection methodology using modal strain energy is more sensitive in detection of the damage than other methods. In practice, the number of sensors is limited due to the environmental and financial conditions. The impact on damage detection performance by reducing the number of sensors is systematically investigated through a series of numerical analyses and the results are discussed. The optimal number of sensor for the integrity estimation of production riser is recommended.

• Journal of Microbiology and Biotechnology
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• 제25권6호
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• pp.782-787
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• 2015

In this study, we developed an assay system for missense mutations in human phenylalanine hydroxylases (hPAHs). To demonstrate the reliability of the system, eight mutant proteins (F39L, K42I, L48S, I65T, R252Q, L255V, S349L, and R408W) were expressed in a mutant strain (pah^-) of Dictyostelium discoideum Ax2 disrupted in the indigenous gene encoding PAH. The transformed pah - cells grown in FM minimal medium were measured for growth rate and PAH activity to reveal a positive correlation between them. The protein level of hPAH was also determined by western blotting to show the impact of each mutation on protein stability and catalytic activity. The result was highly compatible with the previous ones obtained from other expression systems, suggesting that Dictyostelium is a dependable alternative to other expression systems. Furthermore, we found that both the protein level and activity of S349L and R408W, which were impaired severely in protein stability, were rescued in HL5 nutrient medium. Although the responsible component(s) remains unidentified, this unexpected finding showed an important advantage of our expression system for studying unstable proteins. As an economic and stable cell-based expression system, our development will contribute to mass-screening of pharmacological chaperones for missense PAH mutations as well as to the in-depth characterization of individual mutations.

• Korean Journal of Occupational Health Nursing
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• 제26권3호
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• pp.184-196
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• 2017

Purpose: We investigated the effects of emotional labor and workplace violence on various physical and mental health outcomes among female workers. Methods: We obtained data from 24,760 female workers who participated in the 4th Korean Working Conditions Survey (2014). Hierarchical logistic regression analysis was used to analyze the relationships. Results: Female emotional workers were more exposed to workplace violence than were female non-emotional workers. Verbal abuse was the most common type of workplace violence. Logistic regression analyses revealed that (1) emotional labor was significantly associated with higher odds of having musculoskeletal or abdominal pain (physical health outcomes), along with overall fatigue (a mental health outcome), and (2) workplace violence experiences were significantly associated with higher odds of musculoskeletal pain, headache/eye strain, abdominal pain, depression/anxiety disorder, overall fatigue, and insomnia/sleep disturbance, after controlling for covariates. Conclusion: This study demonstrated that both emotional labor and workplace violence have negative effects on physical and mental health. However, workplace violence experience has a stronger negative impact on health outcomes than does emotional labor alone. A management system to eradicate workplace violence and programs aimed at managing emotional labor are urgently needed at the organizational level.