• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.997-1006
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• 2010

For manufacturing modern cars, so-called multi-materials, such as aluminum alloy with high-strength steels, are used. For obtaining such materials, a new joining method is required to achieve the multi-material design. Mechanical clinching is one of joining methods used to join the dissimilar materials. The objective of this study is to investigate the characteristics of mechanical clinching of Al5052 alloy to high-strength steels (SPFC440, 590, 780). Using FE-analysis and clinching experiment, the joinability of Al5052 alloy to high-strength steel is evaluated by geometrical shape of mechanical clinched joint, such as neck-thickness and undercut. Further, the joint strength is evaluated by performing a single-lap shear test. The upper high-strength steel SPFC780 was not clinched because of the necking of the upper sheet. The joint strength increased with increasing strength of the upper sheet. For the lower high-strength steel sheet, the joinability and joint strength decreased with increasing strength of the lower sheet.

• Tunnel and Underground Space
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• v.28 no.1
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• pp.111-124
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• 2018

The purpose of this study is to analyze ventilation design factor for network-type double-deck road tunnel that have been developed actively around the world. A numerical analysis was carried out through computational fluid dynamics (CFD) to derive shock loss coefficient that occurs due to the change in cross sectional area at both merging section and diverging section. The model used for the numerical analysis is real-scale model and the reliability of the result is secured by comparing with the coefficient of the previous studies. As a result of this study, shock loss coefficient was calculated depending on the change in cross-sectional area ratio and was higher than the result of previous studies in case of both merging section and diverging section. It is considered that the characteristics of the geometrical structure of network-type double-deck road tunnel have a great impact on shock loss coefficient. Therefore, the result of this study is expected to be helpful for more accurate ventilation design of network-type double-deck road tunnel.

• The Journal of the Acoustical Society of Korea
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• v.24 no.8
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• pp.469-480
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• 2005

There have been always some difficulties in target setting and conditioning of acoustic performances or the Korean traditional music hall due mainly to the lack of the information on the sound radiation characteristics of Korean musical sources. As the 2nd experiment succeeding the previous study[1], the radiation characteristics of eight typical Korean traditional musical sources were investigated if precision. The selected musical sources were Geomungo, Haegeum (string), Piri, Taepyeongso (woodwind), Buk, Kwaengguari, Jing (drum), and male Pansori Chang (vocal Performance). The results show that the directivity pattern of each instrument is different and has their own directivity characteristics. Measured directional and spectral characteristics of traditional Korean music sources were implemented into the computation of architectural acoustic measures. Significant differences in the acoustic measures at receiver positions were observed between the results in using the omni-directional source and the directional one. In order to investigate the acoustical characteristics of the instruments depending on the spatial variation four different shapes of halls were introduced including rectangular, fan. horse-shoe and geometrical shapes. Room acoustical parameters such as RT, SPL, C80, LF, STI were calculated at each type or hall. As the results, It was found that the rectangular hall has the most high clarity. lateral energy and STI values among low shapes of halls. It is thought that the suggested source data and design method can be used as a basic reference in the future acoustic design of performance halls for the Korean traditional music.

• Journal of the Korean Geotechnical Society
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• v.31 no.4
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• pp.45-55
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• 2015

The stability of the adjcent structures or slopes under blasting is typically evaluated using an empirical vibration attenuation curve or dynamic numerical analysis. To perform a dynamic analysis, it is necessary to determine the blast load and the damping ratio of rock mass. Various empirical methods have been proposed for the blast load. However, a study on representative values of damping ratio of a rock mass has not yet been performed. Therefore, the damping ratio was either ignored or selected without a clear basis in performing a blast analysis. Selection of the dampring ratio for the rock mass is very difficult because the vibration propagation is influenced by the layout and properties of the rock joints. Besides, the vibration induced by blasting is propagated spherically, whereas plane waves are generated by an earthquake. Since the geometrical spreading causes additional attenuation, the damping ratio should be adjusted in the case of a 2D plane strain analysis. In this study, we proposed equivalent damping ratios for use in continuum 2D plane strain analyses. To this end, we performed 2D dynamic analyses for a wide range of rock stiffness and investigated the characteristics of blast vibration propagation. Based on numerical simulations, a correlation between the attenuation equation, shear wave velocity, and equivalent damping ratio of rock mass is presented. This novel approach is the first attempt to select the damping ratio from an attenuation relationship. The proposed chart is easy to be used and can be applied in practice.

• Journal of the Society of Disaster Information
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• v.17 no.4
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• pp.747-754
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• 2021

Purpose: Seismic safety evaluation of a curved bridge must be performed since the curved bridges exhibit the complex behavior rather than the straight bridges, due to geometrical characteristics. In order to conduct the probabilistic seismic assessment of the curved bridge, Seismic fragility evaluation was performed using the uncertainty of the steel material properties of a curved bridge girde, in this study. Method: The finite element (FE) model using ABAQUS platform of the curved bridge girder was constructed, and the statistical parameters of steel materials presented in previous studies were used. 100 steel material models were sampled using the Latin Hypercube Sampling method. As an input ground motion in this study, seismic fragility evaluation was performed by the normalized scale of the Gyeongju earthquake to 0.2g, 0.5g, 0.8g, 1.2g, and 1.5g. Result: As a result of the seismic fragility evaluation of the curved girder, it was found that there was no failure up to 0.03g corresponding to the limit state of allowable stress design, but the failure was started from 0.11g associated with using limit state design. Conclusion: In this study, seismic fragility evaluation was performed considering steel materials uncertainties. Further it must be considered the seismic fragility of the curved bridge using both the uncertainties of input motions and material properties.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.9
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• pp.607-616
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• 2019

Free body diagram analysis is done for key parts of pilot stage of LLV (Load Limit Valve) which is used to protect overload for static structural test of aerospace flight vehicle. It is shown through the analysis that diameter ratio($D_2)^{ten}/D_2)^{comp}$) of two poppets in a pilot stage must be equal to piston area ratio($A_{comp}/A_{ten}$) of a hydraulic actuator for making a poppet open consistently at constant force applied by an actuator. The result of the analysis is verified by measuring geometries of the poppets in the four different LLVs which are corresponding to four actuators with different capacity and have been used after being imported in this laboratory. Results of "Adjuster resolution tests" with two different pilot stages show the max. deviation of Fi(actuator force in instant of opening poppet) from average Fi obtained for each turn of adjuster is 0.3KN and max. deviation of the Fi normalized by average Fi of each turn of adjuster is 3.7%. From the results, it is verified that the two pilot stages with same poppet diameter ratio make a poppet consistently open at Fis within ${\pm}3.7%$ deviation from the average Fi. The deviation is shown to be caused from frictional force of O-ring in the poppet. Additionally, design factors for poppet spring and adjuster, which are also key parts of the pilot stage, are distinguished and procedure for deciding the factors are also shown in this study.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.125-132
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• 2019

This paper presents a seismic reliability analysis method for an offshore wind turbine with a twisted tripod support structure under earthquake loading. A three dimensional dynamic finite element model is proposed to consider the nonlinearity of the ground-pile interactions and the geometrical characteristics of the twisted tripod support structure where out-of-plane displacement occurs even under in-plane lateral loadings. For the evaluation of seismic reliability, the failure probability was calculated for the maximum horizontal displacement of the pile head, which is calculated from time history analysis using artificial earthquakes for the design return periods. The application of the subset simulation method using the Markov Chain Monte Carlo(MCMC) sampling is proposed for efficient reliability analysis considering the limit state equation evaluation by the nonlinear time history analysis. The proposed method can be applied to the reliability evaluation and design criteria development of the offshore wind turbine with twisted tripod support structure in which two dimensional models and static analysis can not produce accurate results.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.7
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• pp.1222-1230
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• 2022

The rotor blade is an important component of a tidal stream turbine and is affected by a large thrust force and load due to the high density of seawater. Therefore, the performance must be secured through the geometrical and structural design of the blade and the blade structural safety to which the composite material is applied. In this study, a 1 MW class large turbine blade was designed using the blade element momentum (BEM) theory. GFRP is a fiber-reinforced plastic used for turbine blade materials. A sandwich structure was applied with CFRP to lay-up the blade cross-section. In addition, to evaluate structural safety according to flow variations, static load analysis within the linear elasticity range was performed using the fluid-structure interactive (FSI) method. Structural safety was evaluated by analyzing tip deflection, strain, and failure index of the blade due to bending moment. As a result, Model-B was able to reduce blade tip deflection and weight. In addition, safety could be secured by indicating that the failure index, inverse reserve factor (IRF), was 1 or less in all load ranges excluding 3.0*Vr of Model-A. In the future, structural safety will be evaluated by applying various failure theories and redesigning the laminated pattern as well as the change of blade material.

• The Journal of Korean Society for Radiation Therapy
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• v.16 no.1
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• pp.1-9
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• 2004

Purpose : The aim of this study is to investigate the properties of small field size and to measure the penumbra and central axis depth dose varying to the jaw setting and off axis distance for indicate this data to small field sizes radiation therapy. Material and methods : The percentage depth dose, beam profile and central axis output dose was measured by farmer type ion chamber and pinpoint chamber using Primart linac with 6MV energy. Beam quality and penumbra variations according to the central axis shift, from center to every 2cm outside increment, and field size, from $1{\times}1cm$ to $10{\times}10cm$ was investigated and compared with that of the standard geometrical condition's results Results : The differences of measured values between two ion chamber was about $37\%$ at 10cm depth with $1{\times}1cm$ field sizes but as field size increased this differences was diminished gradually. Measured data from various off axis distance with the different asymmetric collimations are not changed significantly but as size decreased the dose variation was increased and at $1{\times}1cm$ field size dose difference among off axis distance was as much as $13\%$, and as shallower the measured depth the central axis dose variations among the OAD was increased, penumbra was not changed noticeably depending on off axis distance but the percentage of penumbra from its initial field sizes was strongly dependant on field sizes and penumbra occupation rates of its own field sizes ranging from $6\%$ at $10{\times}10cm$ to $50\%$ at $1{\times}1cm$ field size. Conclusion : For imrt treatment, there are several numbers of different gentry angles with beams of nonuniform fluences are required and several complex factors involved. Among them the characteristics of beam output varying to the geometrical setting and design of collimators are of important to attaining a good treatment results. As mentioned in results the differences of measured values are changed significantly depends on ion chamber volume, depths and field size. For providing quality radiation treatment, especially at small field size, those factor's should have considering deliberately.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.4
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• pp.316-323
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• 2011

Purpose: The purpose of this study was to investigate the effect of different thread designs on the marginal bone stresses around dental implant. Materials and methods: Standard ITI implant(ITI Dental Implant System; Straumann AG, Waldenburg, Switzerland), 4.1 mm in diameter and 10 mm in length, was selected as control. Test implants of four different thread patterns were created based on control implant, i.e. maintaining all geometrical design of control implant except thread pattern. Four thread designs used in test implants include (1) small V-shape screw (model A), (2) large V-shape screw (model B), (3) buttress screw (model C), and (4) trapezoid screw (model D). Surface area for unit length of implant was 14.4 $mm^2$ (control), 21.7 (small V-shape screw), 20.6 (large V-shape screw), 17.0 (buttress screw) and 28.7 $mm^2$ (trapezoid screw). Finite element models of implant/bone complex were created using an axisymmetric scheme with the use of NISA II/DISPLAY III (Engineering Mechanics Research Corporation, Troy, MI, USA). A load of 100 N applied to the central node on the crown top either in parallel direction or at 30 degree to the implant axis (in order to apply non-axial load to the implant NKTP type 34 element was employed). Quantification and comparison of the peak stress in the marginal bone of each implant model was made using a series of regression analyses based on the stress data calculated at the 5 reference points which were set at 0.2, 0.4, 0.6, 0.8 and 1.0 mm from implant wall on the marginal bone surface. Results: Results showed that although severe stress concentration on the marginal bone cannot be avoided a substantial reduction in the peak stress is achievable using different thread design. The peak marginal bone stresses under vertical loading condition were 7.84, 6.45, 5.96, 6.85, 5.39 MPa for control and model A, B, C and D, respectively. And 29.18, 26.45, 25.12, 27.37, 23.58 MPa when subject to inclined loading. Conclusion: It was concluded that the thread design is an important influential factor to the marginal bone stresses.