• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.1
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• pp.42-47
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• 2018

This paper describes the dynamical behavior of the bicycle and its nonlinear effect when magnetic repulsive forces are applied to the bicycle cushion system. A finite-element method was used to obtain its reliabilities by comparing the experimental and numerical values and select the proper magnet sizes. The Equivalent spring stiffness values were evaluated in terms of both linear and nonlinear approximations, where the nonlinear effect was specifically investigated for the ride comfort. The corresponding equations of linear and nonlinear motion were derived for the numerical model with three degrees of freedom. Dynamic behaviors were observed when the bicycle ran over a curvilinear road in the form of a sinusoidal curve. The analysis in this paper for the observed nonlinearity of magnetic repulsive forces will be a useful guide to more accurately predict the cushion design for any vehicle system.

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.151-164
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• 2023

The latest earthquake's costly repairs and economic disruption were brought on by excessive residual drift. Self-centering systems are one of the most efficient ways in the current generation of seismic resistance system to get rid of and reduce residual drift. The mechanics and behavior of the self-centering system in response to seismic forces were impacted by a number of important factors. The amount of post-tensioning (PT) force, which is often employed for the standing posture after an earthquake, is the first important component. The energy dissipater element is another one that has a significant impact on how the self-centering system behaves. Using the damper as a replaceable and affordable tool and fuse in self-centering frames has been recommended to boost energy absorption and dampening of structural systems during earthquakes. In this research, the self-centering steel moment frame connections are equipped with cushion flexural dampers (CFDs) as an energy dissipator system to increase energy absorption, post-yielding stiffness, and ease replacement after an earthquake. Also, it has been carefully considered how to reduce permanent deformations in the self-centering steel moment frames exposed to seismic loads while maintaining adequate stiffness, strength, and ductility. After confirming the FE model's findings with an earlier experimental PT connection, the behavior of the self-centering connection using CFD has been surveyed in this study. The FE modeling takes into account strands preloading as well as geometric and material nonlinearities. In addition to contact and sliding phenomena, gap opening and closing actions are included in the models. According to the findings, self-centering moment-resisting frames (SF-MRF) combined with CFD enhance post-yielding stiffness and energy absorption with the least amount of permeant deformation in a certain CFD thickness. The obtained findings demonstrate that the effective energy dissipation ratio (β), is increased to 0.25% while also lowering the residual drift to less than 0.5%. Also, this enhancement in the self-centering connection with CFD's seismic performance was attained with a respectable moment capacity to beam plastic moment capacity ratio.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.1004-1006
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• 2014

This study was conducted to improve the understanding of factors affecting an automobile seat cushion in dynamic conditions. When there are two dummies on the seat to measure each places respectively at once, the shape of the transfer function changes because the dummies affect each other as if they are linked with some kind of a spring when under excitation. A simple two-degree-of-freedom linear model is used to define a translational stiffness of dynamic coupling phenomenon. The cushion deflection model was created to find the relation between dynamic coupling and distance. Experimental set-up was made to compare with the two-degree-of-freedom linear model. The dynamic coupling factor could be utilized to improve the dynamic comfort of automobile seats.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.5-13
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• 2015

For the bearing capacity evaluation, dynamic pile tests instead of static pile tests have been commonly used in embedded piles, which are known to have low noise and low vibration construction method. The objective of this study is to analyze the bearing capacity and penetration behaviors of embedded piles, which are constructed in different ground conditions, by using force and velocity signals obtained in the final blows during construction of embedded piles. For the dynamic pile analyses, the CAse Pile Wave Analysis Program (CAPWAP) and Wave Equation Analysis of Piles (WEAP) have been commonly used. In this study, the CAPWAP and WEAP are used for the analyses of the dynamic pile tests, which are conducted on embedded piles. The input values, output values, and force-velocity graphs of CAPWAP determined by analyzing the measured force-velocity signals are investigated. In addition, similar force-velocity singals are obtained from the WEAP by analyzing the input values of the WEAP. Considering the subsurface investigation results around the pile tips, if the N-value increases exponentially along the depth, toe quake value should be small, and therefore large bearing capacity is identified. On the contrary, if the N-value increases linearly, the bearing capacity is small because of large toe quake value. Furthermore, the stiffness of hammer cushion and pile cushion, which is difficult to find correct values, is recommended lower than 500 kN/mm. This study demonstrates that the results of WEAP may be similar to those of CAPWAP and the WEAP can be used to estimate the bearing capacity of embedded piles.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.434-437
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• 2007

Cold forging technology of a gear product is being interested in the dimensional accuracy, high stiffness and reduction of stress concentration. Especially it is needed to avoid the damage due to extremely high local pressure. Therefore it is important to ensure high pressure in die design. In this study, single die insert type and splitted die insert type are considered to recognize the notch effects in the die of sprocket forming. The stress concentration has been released at the notch area by the cushion effect in the splitted die insert.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.452-456
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• 2007

Cold forging technology of a gear product is being interested in the dimensional accuracy, high stiffness and reduction of stress concentration. Especially it is needed to avoid the damage due to extremely high local pressure. Therefore it is important to reduce the high pressure in die design of cold forging. In this study, single die insert type and splitted die insert type are considered to recognize the notch effects in the die of sprocket forming. The stress concentration has been released at the notch area by the cushion effect in the splitted die insert.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.251-257
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• 2005

Several air cells are installed in the seat cushion to adjust the stiffness of seat by changing the air pressure. To select proper air pressure in the air cells, two kinds of tests are performed. For the pressure distribution on the seat, the maximum pressure and mean pressure are compared. And for the dynamic ride values, SEAT (Seat Effective Amplitude Transmissibility) values are calculated and compared. These experiments are carried out with three different drivers, three different vehicle speeds on the highway and two different speed on the primary road, and three different air pressures. From the real car tests, optimum air cell pressure depending on the vehicle speed and driver's weight are recommended.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.4
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• pp.193-200
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• 2014

This paper examines the pounding problem between adjacent decks subjected to strong earthquakes. The elastomeric bearings in an isolated bridge reduce the stresses on the superstructure and cushion the impact by transferring smaller seismic forces to the substructure. On the other hand, these bearings also allow large horizontal displacement of the superstructure due to seismic forces. Bridges having various supporting soil conditions and different frequency ratios between adjacent decks are investigated by numerical analysis. In the analysis, decision making is conducted whether the collision took place or not and, the magnitude of pounding force and the duration time of collision are obtained and the results are discussed.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.489-492
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• 2005

Even though the blood pressure is one of the most widely used index for the healthcare monitoring of hypertensive and normotensive persons, there is no non-intrusive measurement method which is commercialized until now. Pulse Arrival Time (PAT) is known that it has close relation with the systolic blood pressure (SBP) and arterial stiffness. In this study, SBP estimation methods by non-intrusive measurement of PAT are suggested. For the unconstrained measurement of PAT, the first method used the electrically non contact electrocardiogram (ENC-ECG) technique and the reflective type of Photoplethysmography (PPG) sensor on the computer mouse. In the second method, ENC-ECG and the air pressure sensor in the seat cushion on a chair were measured. The third method used ECG electrodes and PPG sensors on the toilet seat cover. The validation and regression analysis of the relationship of PAT and SBP are summarized. These methods have considerable errors to be used for all people. But these can be applied for each subject after the parameter customization within acceptable error. So, it is feasible for suggested methods to be used for monitoring of SBP in daily life in non-intrusive way when there is personal identification system of each subject.

• Structural Engineering and Mechanics
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• v.85 no.3
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• pp.407-417
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• 2023

Precast assembled bridge piers with hybrid connection (PASP) use both tendons and socket connections. To study the seismic performance of PASP, a full-scale in-situ test was performed based on an actual bridge project. The elastic-plastic fiber model of PASP was established using finite element software, and numerical analyses were performed to study the influence of prestress degree and socket depth on the PASP seismic performance. The results show that the typical failure mode of PASP under horizontal load is bending failure dominated by concrete cracking at the joint between the column and cushion cap. The cracking of the pier concrete and opening of joints depend on the prestress degree and socket depth. The prestressing tendons and socket connection can provide enough ductility, strength, restoration capability, and bending strength under small horizontal displacements. Although the bearing capacity and post yield stiffness of the pier can be improved to some extent by increasing the prestressing force, ductility is reduced, and residual deformation is increased. Overall, there are reasonable minimum socket depths to ensure the reliability of the socket connection.