• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.4
• /
• pp.92-98
• /
• 2010

Virtual ground modeling is one of key topic for real-time vehicle dynamic simulation. This paper discusses about the virtual 3D road modeling process using parametric surface concept. General road data is a type of lumped position vector so interpolation process is required to compute contact of internal surface. The parametric surface has continuity and linearity within boundaries and functions are very simple to find out contact point. In this paper, the parametric surface formula is adopted to road modeling to calculate road hight. Position indexing method is proposed to reduce memory size and resource possession, and a simple mathematical method for contact patch searching is also proposed. The developed road process program is tested in dynamic driving simulation on off-road. Conclusively, the new virtual road program shows high performance of road hight computation in vast field of off-road simulation.

• Tribology and Lubricants
• /
• v.37 no.5
• /
• pp.195-202
• /
• 2021

This paper presents a numerical analysis of the lubrication characteristics of condensed water molecules on a solid surface by conducting molecular dynamics simulations. We examine two models consisting of a simple hexahedral substrate with and without water molecules to reveal the lubrication mechanism of mono-layered water molecules. We perform a sliding simulation by contacting and translating a single asperity on the substrate under various normal loads. During the simulation, we measure the friction coefficient and atomic stress. When water molecules were interleaved between solid surfaces, atomic stress exerted on individual atom and friction coefficient were smaller than those of model without water molecule. Particularly, at a low load, the efficacy of water molecules in the reduction of atomic stress and friction is remarkable. Conversely, at high loads, water molecules rarely lubricate solid surfaces and fail to effectively distribute the contact stress. We found a critical condition in which the lubrication regime changes and beyond the condition, significant plastic deformation was created. Consequently, we deduce that water molecules can distribute and reduce contact stress within a certain condition. The reduced contact stress prevents plastic deformation of the substrate and thus diminishes the mechanical interlocking between the asperity and the substrate.

• The Southeast Asian review
• /
• v.21 no.2
• /
• pp.1-41
• /
• 2011

Southeast Asia developed maritime trade from the early period due to the suitable physical and cultural conditions. The land consists of peninsular and archipelago, and located at the junction of the two monsoons in South China Sea and India Ocean. The people inherit cultural openness to receive outer influences positively. When Portuguese came to Southeast Asia in 16th century, the region had already enjoyed certain level of commercial development and sociocultural dynamics through the long time experience of interactions with outer world. The Portuguese contact to Southeast Asia was more of participation and assimilation than of conquest and rule experienced in South America. It was due to the higher level of spiritual and material civilization existed in Southeast Asia. Portuguese brought several new elements into Southeast Asia such as colonization and new weapons, Cartaz system and commercial monopoly, and Catholic mission and Casado policy. These new elements, however, did not impact much on the existing Maritime trade that played an important role to change the sociocultural structure of Southeast Asia. Even though Portuguese contact itself did not make significant differences in Southeast Asia, it was meaningful in a sense that it opened a path and left a model case for the more powerful Europeans who came soon after her.

• KDI Journal of Economic Policy
• /
• v.44 no.2
• /
• pp.1-28
• /
• 2022

This paper studies how COVID-19 has affected the labor market in Korea through a general equilibrium model with multiple industries and occupations. In the model, workers are allocated to one of many occupations in an industry, and industrial or occupational shocks alter the employment structure. I calibrate the model with Korean data and identify industrial and occupational shocks, referred to here as COVID-19 shocks, behind the employment dynamics in 2020 and 2021. I find that COVID-19 shocks are more severe for those with jobs with a higher risk of infection and in those that are more difficult to do from home. Interestingly, the relationship between COVID-19 shocks and infection risk weakened as the pandemic progressed, whereas the relationship between COVID-19 shocks and easiness of work-from-home strengthened. I interpret the results as meaning that the pandemic may direct future technological changes to replace tasks that require contact-intensive steps, and I simulate the impact of such technological changes through the lens of the model. The results show that such technological changes will lower the demand for manual workers compared to the demands for other occupations. This contrasts with the earlier trend of job polarization, where manual workers continued to increase their employment share, with the share of routine workers secularly declining at the same time.

• Journal of Hydrogen and New Energy
• /
• v.35 no.2
• /
• pp.205-215
• /
• 2024

This study introduced a direct contact heat exchanger to enhance the efficiency of polymer electrolyte membrane fuel cells (PEMFCs) systems. According to previous research, 28% of the operating costs of fuel cell systems are attributed to heat exchanger devices, prompting the design of a direct contact heat exchanger to address this issue. Optimal configurations were determined through computational fluid dynamics analysis and experimental device fabrication, and the enhanced heat exchange performance of the heat exchanger was experimentally confirmed. Through this, the contribution of the direct contact heat exchanger to the heat management and efficiency enhancement of PEMFC systems was established.

• Journal of Drive and Control
• /
• v.14 no.2
• /
• pp.23-29
• /
• 2017

In this study, a flexible multi-body dynamic simulation model of a knuckle boom crane is developed to evaluate the stress of spindle and rack gears under dynamic working conditions. It is difficult to predict potential critical damage to a knuckle boom crane if only the static condition is considered during the development process. To solve this issue, a severe working scenario (high speed with heavy load) was simulated as a boundary condition for testing the integrity of the dynamic simulation model. The crane gear model is defined as a flexible body so contact analysis was performed. The functional motion of a knuckle boom crane is generated by applying forces at each end of the rack gear, which was converted from hydraulic pressure measured for the experiment. The bending and contact stress of gears are theoretically calculated to validate the simulation model. In the simulation, the maximum stress of spindle and rack gears are observed when the crane abruptly stops. Peak impact force is produced at the contact interface between pinion and rack gears due to the inertia force of the boom. However, the maximum stress (bending/contact) of spindle and rack are under the yield stress, which is safe from damage. By using the developed simulation model, the experiment process is expected to be minimized.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.10a
• /
• pp.515-516
• /
• 2009

• 제어로봇시스템학회:학술대회논문집
• /
• 1991.10a
• /
• pp.588-588
• /
• 1991

This paper proposes a compliance robot control algorithm using fuzzy adaptive controller and fuzzy compliance vector generator. In the compliance robot control, we need more adaptivity because the linear modeling in robot dynamics is getting more difficult by contact with external environment. Existing adapitive controllers have difficulty in realtime processing. So in order to overcome it, We adopt fuzzy adaptive controller and propose fuzzy compliance vector generator for flexible compliant motion. We analyze and confirm the proposed algorithm by surface processing experiment with a control system implemented by VME system.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2001.04a
• /
• pp.489-494
• /
• 2001

This paper deals with a dynamic modeling of artillery system loaded by gun charge explosion during firing condition. Geometric and elastic gun data are used to modify a projectile interaction model. The maximum impact force on gun barrel was 15,000 N and the gun barrel moved about 1.3 m. A cannon bal] was presented to travel in the flexible gun, the traveling distance was about 23,000 m, and the angular velocity was about 10rad/sec. The artillery dynamic system using the multi-body dynamics enables us to obtain the data for the fatigue analysis.

• Geomechanics and Engineering
• /
• v.21 no.1
• /
• pp.23-33
• /
• 2020

An advancing cutting roof for gob-side entry retaining with no-pillar mining under specific geological conditions is more conducive to the safe and efficient production in a coalmine. This method is being promoted for use in a large number of coalmines because it has many advantages compared to the retaining method with an artificial filling wall as the gateway side filling body. In order to observe the inner structure of the gateway cutting roof and understand its stability mechanism, an equivalent material simulation experiment for a coalmine with complex geological conditions was carried out in this study. The results show that a "self-stabilization bearing structure" equilibrium model was found after the cutting roof caving when the cut line deviation angle was unequal to zero and the cut height was greater than the mining height, and the caving roof rock was hard without damage. The model showed that its stability was mainly controlled by two key blocks. Furthermore, in order to determine the optimal parameters of the cut height and the cut line deviation angle for the cutting roof of the retaining gateway, an in-depth analysis with theoretical mechanics and mine rock mechanics of the model was performed, and the relationship between the roof balance control force and the cut height and cut line deviation angle was solved. It was found that the selection of the values of the cut height and the cut line deviation angle had to conform to a certain principle that it should not only utilize the support force provided by the coal wall and the contact surface of the two key blocks but also prevent the failure of the coal wall and the contact surface.