• Steel and Composite Structures
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• v.50 no.1
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• pp.15-24
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• 2024

This research presents dynamical reaction investigation of pore-dependent and nano-thickness beams having functional gradation (FG) constituents exposed to a movable particle. The nano-thickness beam formulation has been appointed with the benefits of refined high orders beam paradigm and nonlocal strain gradient theory (NSGT) comprising two scale moduli entitled nonlocality and strains gradient modulus. The graded pore-dependent constituents have been designed through pore factor based power-law relations comprising pore volumes pursuant to even or uneven pore scattering. Therewith, variable scale modulus has been thought-out until process a more accurate designing of scale effects on graded nano-thickness beams. The motion equations have been appointed to be solved via Ritz method with the benefits of Chebyshev polynomials in cosine form. Also, Laplace transform techniques help Ritz-Chebyshev method to obtain the dynamical response in time domain. All factors such as particle speed, pores and variable scale modulus affect the dynamical response.

• Journal of the Korea Convergence Society
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• v.8 no.9
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• pp.365-372
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• 2017

Squat exercise is one of the important free weight exercises that can safely and effectively expect the athletic performance by establishing the rationale. Therefore, it is necessary to study the side effects caused by incorrect exercise, scientific countermeasures and to develop a exercise estimation model. It is effective and accurate to use a variety of assistive devices to calibrate athletic posture. The issues of the structural analysis for designing a foot plate for squat exercise is to model the behavior by the dynamic behavior. It should be consider that the center of gravity of each segmented body is different when the maximum load is applied. It is applied to complete system design through simulation method with kinematic dynamic, ground reaction force and load analysis for the free weight exercise equipment, VR device, and safety foot plate. In this paper, the authors propose the design method for the vertical load distribution applied in the design of the foot plate used for the squat exercise mechanism, and based on these results, design make the more safe and reliable free weight exercise equipment system.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.429-438
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• 2011

In this study, the explicit numerical algorithm was proposed to simulate the stress erection process and ultimate-load analysis of the strarch (stressed arch) system. The strarch system is a unique and innovative structural system and member prestress comprising prefabricated plane truss frames erected through a post-tensioning stress erection procedure. The flexible bottom chord, which has sleeve and gap details, is closed by the reaction force of the prestressing tendon. The prestress imposed on the tendon will enable the strarch system to be erected. This post-tensioning process is called "stress erection process." During this process, plastic rigid-body rotation occurs to the flexible top chord due to the excessive amount of plastic strain, and the structural characteristic is unstable. In this study, the dynamic relaxation method (DRM) was adopted to calculate the nonlinear equilibrium equation of the system, and a displacement-based finite-element-formulated filament beam element was used to simulate the nonlinear behavior of the top chord sections of the strarch system. The section of the filament beam element was composed by the amount of filaments, which can be modeled by various material models. The Ramberg-Osgood and bilinear kinematic elastic plastic material models were formulated for the nonlinear material behaviors of the filaments. The numerical results that were obtained in the present study were compared with the experiment results of the stress erection and with the results of the ultimate-load analysis of the strarch unit frame. The results of the present studies are in good agreement with the previous experiment results, and the explicit DRM enabled the analysis of the post-buckling behaviors of the strarch unit frame.

• Journal of the Korean GEO-environmental Society
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• v.24 no.9
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• pp.33-40
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• 2023

The lateral load which is applied to the pile foundation supporting the superstructure during an earthquake is divided into the inertia force of the upper structure and the kinematic force of the ground. The inertia force and the kinematic force could cause failure to the pile foundation through different complex mechanisms. So it is necessary to predict and evaluate interaction of the ground-pile-structure properly for the seismic design of the foundation. The interaction is affected by the lateral behavior of the structure, the length of the pile, the boundary conditions of the head, and the relative density of the ground. Confining pressure and ground stiffness change accordingly when the relative density changes, and it results that the coefficient of subgrade reaction varies depending on each system. Horizontal bearing behavior and capacity of the pile foundation vary depending on lateral load condition and relative density of the sandy soil. Therefore, the 1g shaking table tests were conducted to confirm the effect of the relative density of the dried sandy soil to dynamic behavior of the group pile supporting the superstructure. The result shows that, as the relative density increases, maximum acceleration of the superstructure and the pile cap increases and decreases respectively, and the slope of the p-y curve of the pile decreases.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.115-116
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• 2002

This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.3
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• pp.237-242
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• 2014

Recently much research are has been done into the compositions of lead-free solders. As a result, there has been a rapid increase in the number of new compositions. In the past, the properties of these new compositions were determined and verified through drop-impact tests. However, these drop tests were expensive and it took a long time to obtain a result. The main goal of this study was to establish an analytical method capable of predicting the impact life-time of a new solder composition for board-level flip chips though the application of drop simulations using LS-DYNA. Based on the reaction load obtain with LS-DYNA, the drop-impact fracture cycles were predicted. The study was performed using a Sn-3.0Ag-0.5Cu solder (305 composition). To verify the reliability of the proposed analytical method, the results of the drop-impact tests and life-time analysis were compared, and were found to be in good agreement. Thus, the new analytical method was shown to be very useful and effective.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.4
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• pp.236-244
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• 2021

Fuel cell systems for medium duty truck require high power demands under driving. Since high power demands results in significant heat generation, thermal management is crucial for the performance and durability of medium duty truck. Therefore, various configurations of dual stacks with cooling systems are investigated to understand appropriate thermal management conditions. The simulation model consists of a dynamic fuel cell stack model, a cooling system model equipped with a controller, and the mounted controller applies a feedback controller to control the operating temperature. Also, In order to minimize parasitic power, the comparison of the cooling systems involved in the arrangement was divided into three case. As a result, this study compares the reaction of fuel cells to the placement of the cooling system under a variety of load conditions to find the best placement method.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1610-1615
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• 2007

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1903-1908
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• 2008

This paper presents a characteristics of linear induction motor considering airgap variation for railway transit in order to achieve high performance of the vehicle. The operating principle of a LIM(Linear induction motor) is identical to a rotary induction motor. Space-time variant magnetic fields are generated by the primary part across the airgap and induce the electro-motive force(EMF) in the secondary part, a conducting sheet. This EMF generates the eddy currents, which interact with the airgap flux and so produce the thrust force known as Loren's force. Even though the operating principal is exactly same as a rotary motor, the linear motor has a finite length of the primary or secondary parts and it causes static and dynamic end-effect which is the discontinuous airgap flux phenomenon. This end-effect causes the deterioration of the system performance, especially in high-speed operation. Another problem is that construction tolerance restricts the minimum airgap in order to prevent a collision between the primary part and the secondary reaction plate. More over, as the airgap length is getting smaller, the attraction force between the primary part and secondary parts is getting larger dramatically and the attraction force would be another friction against propulsion. Therefore, it is necessary to figure out the characteristics of linear induction motor considering airgap variation in order to achieve high performance of the vehicle. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction and thrust force according to the airgap variation is analyzed. The simulation results are presented to show the effect of the LIM according to the airgap variation.

• Archives of Plastic Surgery
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• v.33 no.6
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• pp.688-694
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• 2006

Purpose: Reconstruction of the craniofacial defects can be carried out with autogenous tissues, allogenic implants, or alloplastic materials. Titanium mesh systems have been used for bony reconstruction in non load-bearing areas. They offer several advantages: immediate availibility without any donor site morbidity, easy handling, stable 3-D reconstruction, and low susceptibility to infection. The aim of this study is to evaluate the usefulness and complications of titanium mesh system in the reconstruction of the craniofacial defects. Methods: From Jan. 2000, to Dec. 2004, we performed reconstruction of craniofacial bone defects in 21 patients who had benign or malignant tumor and fracture events in the cranium, orbit, nasal bone, maxilla, zygoma and the mandible. The size of the defects ranged from $1.0{\times}1.5cm$ to $12{\times}10cm$. Two different mesh systems, micro-titanium augmentation mesh and dynamic mesh was used for bony reconstruction in non load-bearing areas. The patients were evaluated from 1 to 4 yrs clinically and radiographically with a mean follow up period of 1.5 yrs. Results: There were no serious complications, including wound infection, foreign body reaction, exposures or loos of the mesh, central infection and pathologic findings of bone around mesh exception of one patient, who had expired of skull base tumor recurrence. Long-term stability of the reconstructions and the overall functional and aesthetic outcome was excellent. Conclusion: Our experiences demonstrate that the Titanium mesh system is a relatively safe and efficient method in the craniofacial reconstruction and have broadens our choices of therapeutic procedures in the craniomaxillofacial surgery.