• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.5
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• pp.343-349
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• 2013

Crashworthy fuel cells have a great influence on improving the survivability of crews. Since 1960's, the US army has developed a detailed military specification, MIL-DTL-27422, defining the performance requirements for rotorcraft fuel cells. In the qualification tests required by MIL-DTL-27422, the crash impact test should be conducted to verify the crashworthiness of fuel cell. Success of the crash impact test means the improvement of survivability of crews by preventing post-crash fire. But, there is a big risk of failure due to huge external load in the crash impact test. Because the crash impact test itself takes a long-term preparation efforts together with costly fuel cell specimens, the failure of crash impact test can result in serious delay of a entire rotorcraft development. Thus, the numerical simulations of the crash impact test has been required at the early design stage to minimize the possibility of trial-and-error with full-scale fuel cells. Present study performs the numerical simulation using SPH(smoothed particle hydro-dynamic) method supported by a crash simulation software, LS-DYNA. Test condition of MIL-DTL-27422 is reflected on analysis and material data is acquired by specimen test of fuel cell material. As a result, the resulting equivalent stresses of fuel cell itself are calculated and vulnerable areas are also evaluated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1166-1176
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• 2011

The prospect in opening the arctic trade transportation route on a year-round basis offers vast opportunity of exploring untapped resources and shortened navigational routes. In addition, the environment's remoteness and lack of technical experiences remains a big challenge for the maritime industry. With this, engine designers and makers are continually investigating, specifically optimizing propulsion shafting system design, to meet the environmental and technical challenges of the region. The International Association of Classification Society, specifically machinery requirements for polar class ships(IACS UR13), embodies the propulsion shafting design requirements for ice class vessels. However, the necessity to upgrade the various features of the unified rules in meeting current polar requirements is acknowledged by IACS and other classification societies. For the polar class propulsion shafting system, it is perceived that the main source of excitation will be the propeller - ice load interaction. The milling - and the impact load, in addition to the load cases interpreted by IACS, contribute greatly to the overall characteristic of the system and due considerations are given during the propulsion design stage. This paper will expound on the excitation load estimation factors affecting the dynamic response of the different propulsion shafting system design. It is anticipated that detailed understanding of these factors will have a significant role during propulsion shafting design in the future.

• Nuclear Engineering and Technology
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• v.25 no.3
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• pp.353-360
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• 1993

Many types of pipe whip restraints are installed to protect the structural components from the anticipated pipe whip phenomena of high energy lines in nuclear power plants. It is necessary to investigate these phenomena accurately in order to design the pipe whip restraints properly and/or to evaluate the acceptability of the pipe whip restraint design. Various research programs have been conducted in many countries to develop analytical methods and to verify the validity of the methods. In this study, various types of finite elements in ANSYS[1], the general purpose finite element computer program, was used to simulate the postulated pipe whips to obtain impact loads and the calculated results were compared with the specific experimental results from the sample pipe whip test for the U-shaped pipe whip restraints. Some calculational models, having the gap element or the spring element between the pipe whip restraint and the pipe line, give reasonably good transient responses of the restraint forces compared with the experimental results, and could be useful in evaluating the acceptability of the pipe whip restraint design.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.549-555
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• 2021

Open hole strength of composite laminates is often used as the design allowable strength for designing composite aircraft structures, particularly those structures subjected to impact loading. Generally, the degradation of strength due to a barely visible impact damage (BVID) is assumed as the strength of 6.0 mm hole diameter in 24.0 mm width specimen. In this study, the residual strength static tests of composite laminates containing circular holes have been performed to investigate the effects of fiber orientation structure on open hole strength. The point stress criterion using a characteristic length is used to predict the open hole strength. The finite element analysis has been used to validate the analytical method. From the test results, it is shown that the characteristic length is related to the percentage of 0°, ±45° and 90° plies of the laminate. And regression analysis has performed to determine the characteristic length and strength of no hole specimens on the arbitrary layup pattern.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.8
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• pp.759-769
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• 2013

Electronic equipment has been applied to virtually every area associated with commercial, industrial, and military applications. Specifically, electronics have been incorporated into avionics components installed in aircraft. This equipment is exposed to dynamic loads such as vibration, shock, and acceleration. Especially, avionics components installed in a helicopter are subjected to simultaneous sine and random base excitations. These are denoted as sine on random vibrations according to MIL-STD-810F, Method 514.5. In the past, isolators have been applied to avionics components to reduce vibration and shock. However, an isolator applied to an avionics component installed in a helicopter can amplify the vibration magnitude, and damage the chassis, circuit card assembly, and the isolator itself via resonance at low-frequency sinusoidal vibrations. The objective of this study is to investigate the dynamic characteristics of an avionics component installed in a helicopter and the structural dynamic modification of its tray plate without an isolator using both a finite element analysis and experiments. The structure is optimized by dynamic loads that are selected by comparing the vibration, shock, and acceleration loads using vibration and shock response spectra. A finite element model(FEM) was constructed using a simplified geometry and valid element types that reflect the dynamic characteristics. The FEM was verified by an experimental modal analysis. Design parameters were extracted and selected to modify the structural dynamics using topology optimization, and design of experiments(DOE). A prototype of a modified model was constructed and its feasibility was evaluated using an FEM and a performance test.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.44-56
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• 1989

Recently the residual strength of damaged tubulars under axial compression has extensively been investigated. However, in spite of the possibility of damage onto underwater members of offshore structures as results of collisions, dropped objects and other accidental impacts occurring in service or during fabrication or installation, no research works on the structural behaviour of damaged tubulars under combined loadings including hydrostatic pressure have been reported in the literature. In this paper, a numerical method has been proposed to estimate the residual strength of damaged tubulars under combined loadings, and then the proposed method has been substantiated with corresponding test data. A simple design equation has been derived based upon the results of the parametric study using the proposed method. The accuracy of the predictions using the derived equation is found to be a 10.1% COV(Coefficient of Variation) together with an 1. 037 mean comparing with the test data.

• Journal of the Korean Society for Railway
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• v.17 no.4
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• pp.260-269
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• 2014

Transition tracks are an alternative for enhancing the long-term serviceability and durability of concrete track components in railway bridges. The goal of this paper is to investigate the structural behavior for transition track systems of railway bridge deck ends. In this study, the structural behavior of transition tracks such as the variations in static, dynamic, and fatigue behaviors and dynamic properties (natural frequency and damping ratio) are assessed and compared through performing loading tests and finite element analyses using actual vehicle impact loadings. As a result, it is found that the structural behavior of the transition track system is expected to satisfy the actual vehicle impact loading, and the variation in the neutral axis and dynamic characteristics are not affected by the fatigue loading. Therefore, it is inferred that the structural capacity and long-term durability of the transition track system is proven.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.83-95
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• 2020

In order to evaluate the stability of the geo-structure of railway bridge, the response dominant frequency was analyzed based on a series of impact vibration load test results. The specifications of the experiment piers were obtained by referring to the completion design data, and when data was missing, a field study was conducted. The impact vibrations test according to the scouring progress was carried out at one pier scheduled to be abandoned, and it was confirmed that the response dominant frequency can be utilized as an evaluation index for scour. In addition, the response dominant frequency was measured through an impact load test at 46 piers in 5 bridges in operation, and the scour safety of the bridge was evaluated by comparing it with the japanese proposal formula.

• Journal of the Korean Institute of Gas
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• v.13 no.4
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• pp.27-32
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• 2009

This paper presents the stress and deformation behaviors using the finite element method as a function of the thickness of the helmets without the bead frames on the top of the shell structure. The helmet that would provide head and neck protections without causing discomfort to the user when it was worn for long periods of time should be manufactured for increasing the safety and impact energy absorption. The FEM computed results show that when the impulsive force is applied on the top surface of a helmet, the maximum stress and strain have been occurred around the position of an applied impact force, which may lead to the initial failure on the top surface of the helmet shell. As the helmet thickness is decreased from 4mm to 2mm, the impact energy absorbing rate is radically increased, and the maximum stress of the helmet is increased over the tensile strength, 54.3MPa of the thermoplastic material. Thus, the top surface of the helmet should be supported by a bead frame and increased thickness of the shell structure.

• Transactions of the KSME C: Technology and Education
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• v.3 no.1
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• pp.37-44
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• 2015

In this paper dynamic deformation of lower hinge of refrigerator is simulated using dynamic finite element analysis while refrigerator is being dropped. The flow stress curves considering velocity dependency of hinge and lower packing material are determined through bending test and compression test at several dropping speeds. The determined material properties and flow stress from reverse engineering were used as input data for refrigerator's drop test using a dynamic finite element analysis software LS-DYNA. Additionally the result between CAE and 3D deformation measurement from real refrigerator drop test are compared and the result shows that the proposed analysis model is very useful to design lower hinge and lower packing endurable to the impulsive drop impact.