• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1163-1169
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• 2014

In this study, a fatigue assessment method for vehicle suspension systems having welded geometries was established under a bending loading condition. For the fatigue life estimation of the actual product's welded joints made of different steels, bending fatigue tests were performed on welded specimens with a simplified shape for obtaining the moment-fatigue-life plot. Further, geometry modeling of the simplified welded specimens was conducted. Results of finite element analysis were used to obtain the stress-fatigue-life plot. The analysis results were also used to calculate the stress concentration factors for notch-factor-based fatigue life estimation. The test results were compared with results of the general notch-factor-based fatigue life estimation for improving fatigue assessment. As a result, it was concluded that both the welded fatigue tests and the notch-factor-based fatigue life estimation are necessary for accurate fatigue assessment.

• Wind and Structures
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• v.20 no.2
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• pp.213-236
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• 2015

For high-speed railways (HSR) in wind prone regions, wind barriers are often installed on bridges to ensure the running safety of trains. This paper analyzes the effect of wind barriers on the running safety of a high-speed train to cross winds when it passes on a bridge. Two simply-supported (S-S) PC bridges in China, one with 32 m box beams and the other with 16 m trough beams, are selected to perform the dynamic analyses. The bridges are modeled by 3-D finite elements and each vehicle in a train by a multi-rigid-body system connected with suspension springs and dashpots. The wind excitations on the train vehicles and the bridges are numerically simulated, using the static tri-component coefficients obtained from a wind tunnel test, taking into account the effects of wind barriers, train speed and the spatial correlation with wind forces on the deck. The whole histories of a train passing over the two bridges under strong cross winds are simulated and compared, considering variations of wind velocities, train speeds and without or with wind barriers. The threshold curves of wind velocity for train running safety on the two bridges are compared, from which the windbreak effect of the wind barrier are evaluated, based on which a beam structure with better performance is recommended.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.9
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• pp.861-868
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• 2017

In this study, a novel magnetic field generator, using a shielding effect for controlling the dynamic stiffness and damping of magnetorheological gels, is proposed. A magnetorheological gel is a smart material that can alter its stiffness and damping, and it can be used as a vibration absorber and in vehicle suspension. It is necessary to control the magnetic field to use magnetorheological gels in various applications. There are two types of magnet field generators, namely the electromagnet and permanent magnet, and the electromagnet is generally used in practical applications. However, owing to its limitations, the electromagnet is not suitable for long-term use. Therefore, in this paper, a novel magnetic field generator is proposed to address such problems for use in real applications.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.437-442
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• 2012

To analyze a multibody system, this paper proposes an implicit numerical integration method for joint coordinates subsystem synthesis method. To verify the proposed method, a multibody model for an unmanned robot vehicle, which consists of six identical independent suspension systems, is developed. The symbolic method is applied to compute the system Jacobian matrix for the implicit integration method. The proposed method is also verified by performing rough terrain run-over simulation in comparison with the conventional implicit integration method. In addition, to evaluate the efficiency of the proposed method, the CPU time obtained by using this method is compared with that obtained by using the conventional implicit method.

• Korean Journal of Veterinary Research
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• v.53 no.2
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• pp.95-101
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• 2013

The study was carried out to evaluate and compare the immune responses in mice experimentally infected with either wild-type or isogenic mutants of Salmonella enterica serovars Enteritidis (SE), Salmonella Typhimurium (ST) and Gallinarum (SG). The mutant strains were constructed by allelic replacement of some virulence-associated genes in the wild-type strains. Seven-week-old female BALB/c mice were orally or intraperitoneally inoculated by injecting bacterial suspension. To evaluate the immune responses, enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunospot (ELISPOT) assay were conducted with serum and fecal samples. As a result, the mice group infected orally with the SE mutant strain showed the highest level of specific IgA-secreting splenocytes, compared to the other groups. The peritoneally injected groups showed the greater levels of IgG1 than the orally injected groups, which was in a good agreement with the previous studies. In addition, the mutant infected groups had the similar secretion levels of antibodies with the wild-type infected groups. These results demonstrated that the SE mutant strain elicited humoral immune response as much as wild-type, implying that it can be useful as a delivery vehicle as well as a candidate of a live attenuated vaccine.

• Elastomers and Composites
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• v.49 no.4
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• pp.293-304
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• 2014

Rubber air spring (RAS) is a special suspension device for the industries of automobile, railroad car and other transportation. A RAS serves as a spring component with the elastic effect of compression and expansion of air in a composite rubber bag. The main component of RAS is the rubber sleeve. Rubber sleeve is the composite which is made up of combination of chloroprene rubber (CR) and nylon 6 cord, and the adhesive strength between CR and nylon 6 cord is very important. In this study, considering the effects of additives in rubber sleeve, various physical properties were tested to find the optimal combination of composition and conditions. Further, in order to select the optimum orientation of the reinforcing fibers, numerical analysis was performed using the finite elements method. After assembling all components of RAS, it was mounted on an actual vehicle, and then it was tested air leakage, fatigue life and fundamental properties.

• Elastomers and Composites
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• v.43 no.1
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• pp.25-30
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• 2008

A bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is a hollow cylinder, which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the force and moment applied to the shaft and the relative deformation and rotational angle of a bushing exhibits features of viscoelasticity. Since a moment-rotational angle relation for a bushing is important for multibody dynamics numerical simulations, the simple relation between the moment and rotational angle has been derived from experiment. It is shown that the predictions by the proposed moment-rotational angle relation are in very good agreement with the experimental results.

• Smart Structures and Systems
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• v.23 no.6
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• pp.615-626
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• 2019

Inerter-based damping devices (IBBDs), which consist of inerter, spring and viscous damper, have been extensively investigated in vehicle suspension systems and demonstrated to be more effective than the traditional control devices with spring and viscous damper only. In the present study, the control performance on cable vibration reduction was studied for four different inerter-based damping devices, namely the parallel-connected viscous mass damper (PVMD), series-connected viscous mass damper (SVMD), tuned inerter dampers (TID) and tuned viscous mass damper (TVMD). Firstly the mechanism of the ball screw inerter is introduced. Then the state-space formulation of the cable-TID system is derived as an example for the cable-IBBDs system. Based on the complex modal analysis, single-mode cable vibration control analysis is conducted for PVMD, SVMD, TID and TVMD, and their optimal parameters and the maximum attainable damping ratios of the cable/damper system are obtained for several specified damper locations and modes in combination by the Nelder-Mead simplex algorithm. Lastly, optimal design of PVMD is developed for multi-mode vibration control of cable, and the results of damping ratio analysis are validated through the forced vibration analysis in a case study by numerical simulation. The results show that all the four inerter-based damping devices significantly outperform the viscous damper for single-mode vibration control. In the case of multi-mode vibration control, PVMD can provide more damping to the first four modes of cable than the viscous damper does, and their maximum control forces under resonant frequency of harmonic forced vibration are nearly the same. The results of this study clearly demonstrate the effectiveness and advantages of PVMD in cable vibration control.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1339-1347
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• 2015

This study discusses a remote control torch system equipped with a GMAW double wire reel. The welding machine is 30m away from the wire feeder at the industrial site and the feeder is three to five meters away from the torch. Accordingly, the welders cannot control the current and voltage that meets the welding condition during work when they are working at a place that prevents them from seeing the control panel, such as inside a vehicle or tank or at a far work site. They also have no choice but to stop working to change the wire reel when it is burned out completely. Such work suspension resulting from frequent moves to adjust the current and voltage as well as to replace the wire and subsequent cooling causes welding defects. This study produced a remote control torch equipped with a double wire reel by simplifying and streamlining the existing GMAW functions to reduce the troubling issue. The remote control torch equipped with a double wire reel and the existing $CO_2$ /MAG welding torch were applied as a V-groove butt in the vertical position using 6mm rolled steel for a SM50A welding structure. After welding, the condition of welded surface beads underwent a visual inspection and radiographic inspection to analyze the welding quality inside the welded part. This study also evaluated the reduction of welding defects, cost saving, the replacing performance against the existing commercial welders, and the effects on possible compatibility.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.86-92
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• 2017

In this study, a running performance evaluation and roller rig test was conducted to evaluate the applicability of a composite bogie frame, which has the role of the primary suspension. The composite bogie frame was made of a GEP224 glass/epoxy prepreg. Vehicle dynamic analysis was carried out on the composite bogie with three different kinds of side beam thicknesses (50 mm, 80 mm, and 150 mm). From the results, the composite bogie with a side beam thickness of 80 mm satisfied all the dynamic design requirements. Although the composite bogie with the side beam thickness of 50mm also met the design requirements, its critical speed was just a 2% margin to the requirement. In contrast, the model of the side beam thickness of 150mm did not meet the ride comfort. In addition, a composite bogie frame with the side beam thickness of 80 mm was fabricated and installed on a complete bogie. Moreover, the roller rig test using the fully equipped bogie was performed to evaluate the critical speed. During the test, the lateral excitation was imposed on the wheelsets to realize the rail irregularity. There was no divergence of the lateral displacement of the wheelsets while increasing the speed. The measured critical speed was similar to the predicted result.