• Geomechanics and Engineering
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• v.12 no.2
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• pp.295-312
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• 2017

Cast in situ and grouted concrete helical piles with 150-200 mm diameter half cylindrical ribs have become an economical and effective choice in Shanghai, China for uplift piles in deep soft soils. Though this type of pile has been successful used in practice, the reinforcing mechanism and the contribution of the ribs to the total resistance is not clear, and there is no clear guideline for the design of such piles. To study the inclusion of ribs to the contribution of shear resistance, the shear behaviour between silty sand and concrete slabs with parallel ribs at different spacing and angles were tested in a large direct shear box ($600mm{\times}400mm{\times}200mm$). The front panels of the shear box are detachable to observe the soil deformation after the test. The tests were modelled with three-dimensional finite element method in ABAQUS. It was found that, passive zones can be developed ahead of the ribs to form undulated failure surfaces. The shear resistance and failure mode are affected by the ratio of rib spacing to rib diameter. Based on the shape and continuity of the failure zones at the interface, the failure modes at the interface can be classified as "punching", "local" or "general" shear failure respectively. With the inclusion of the ribs, the pull out resistance can increase up to 17%. The optimum rib spacing to rib diameter ratio was found to be around 7 based on the observed experimental results and the numerical modelling.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.411-421
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• 2018

Although a rubber isolation cushion can reduce the dynamic response of a structure itself, it has little influence on the height of a sloshing wave and even may induce magnification action. Vertical baffles are set into a base-isolated Concrete Rectangular Liquid Storage Structure (CRLSS), and baffles are opened as holes to increase the energy dissipation of the damping. Problems of liquid nonlinear motion caused by baffles are described using the Navier-Stokes equation, and the space model of CRLSS is established considering the Fluid-Solid Interaction (FSI) based on the Finite Element Method (FEM). The dynamic response of an isolated CRLSS with various baffles under an earthquake is analyzed, and the results are compared. The results show that when the baffle number is certain, the greater the number of holes in baffles, the worse the damping effects; when a single baffle with holes is set in juxtaposition and double baffles with holes are formed, although some of the dynamic response will slightly increase, the wallboard strain and the height of the sloshing wave evidently decrease. A configuration with fewer holes in the baffles and a greater number of baffles is more helpful to prevent the occurrence of two failure modes: wallboard leakage and excessive sloshing height.

• Journal of the Korean Magnetics Society
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• v.17 no.6
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• pp.242-245
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• 2007

Conduction noise attenuation by composite sheets of high magnetic and dielectric loss has been analyzed by using electromagnetic field simulator which employs finite element method. The simulation model consists of microstrip line with planar input/output ports and noise absorbers (magnetic composite sheets containing iron flake particles as absorbent fillers). Reflection and transmission parameters $(S_{11}\;and\;S_{21})$ and power loss are calculated as a function of frequency with variation of sheet size and thickness. The simulated value is in good agreement with measured one and it is demonstrated that the proposed simulation technique can be effectively used in the design and characterization of noise absorbing materials in the RF transmission lines.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.103-108
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• 2008

Magnetoresistive random access memory (MRAM) don't get very public face on the field of non-volatile memory. Because recording capacity of MRAM is smaller than other non-volatile memory and structurally, magnetic efficiency of MRAM is very bad. We diminish a size of one cell in order to make MRAM of high recording capacity. But It don't make high recording field in general structures consisting of two current wire. Accordingly, We make a cell of small size is impossible. In this paper, we suggest new MRAM that it have two pole of high permeability on both ends of recording layer. Because magnetic efficiency of new MRAM is higher than exiting MRAM, it can make high recording field. And we can diminish the size of one cell due to recording layer of high coercivity. We used three-dimension finite element method to prove the reliability.

• Journal of Aerospace System Engineering
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• v.12 no.2
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• pp.1-6
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• 2018

The torque ripple that is generated by the irregularity of magnetic flux density on the BLDC motor in a satellite actuator degrades the satellite attitude control performance. In this paper, the performance analysis of permanent magnet configurations (shape, arrangement, and air gap) is simulated by the Finite Element Method (FEM) to find the appropriate combination of the configuration. The configuration is chosen by comparing between rectangular and arc-shaped permanent magnets and single-arrangement and dual-arrangement magnets. The performance is verified by a prototype.

• Journal of Biomedical Engineering Research
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• v.19 no.5
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• pp.495-502
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• 1998

A mathematical model of viscoelasticity on the material property of human pharyngeal tissue utilizing Y.C. Fung's Quasi-linear viscoelastic theory is proposed based on cyclic load, stress relaxation, incremental load, and uniaxial tensile load tests. The material properties are characterized and compared with other biological materials' results. The mathematical model is proposed by combining two characteristic functions determined from the stress relaxation and uniaxial tensile load tests. The reduced stress relaxation function G(t) and elastic response function S(t) are obtained from stress relaxation test and uniaxial tensile load test results respectively. Then the model describing stress-time history of the tissue is implemented utilizing two functions. The proposed model is evaluated and validated by comparing the model's cyclic behaviour with experimental results. The model data could be utilized as an important information for constructing 3-dimensional biomechanical model of human pharynx using FEM(Finite Element Method).

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.337-341
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• 2010

In this paper, an extremely low voltage operated micro corner cube retroreflector (CCR) was fabricated for free-space optical communication applications by using bulk silicon micromachining technologies. The CCR was comprised of an orthogonal vertical mirror and a horizontal actuated mirror. For low voltage operation, the horizontal actuated mirror was designed with two PZT cantilever actuators, torsional bars, hinges, and a mirror plate with a size of $400{\mu}m{\times}400{\mu}m$. In particular, the torsional bars and hinges were carefully simulated and designed to secure the flatness of the mirror plate by using a finite element method (FEM) simulator. The measured tilting angle was approximately $2^{\circ}$ at the applied voltage of 5 V. An orthogonal vertical mirror with an extremely smooth surface texture was fabricated using KOH wet etching and a double-SOI (silicon-on-insulator) wafer with a (110) silicon wafer. The fabricated orthogonal vertical mirror was comprised of four pairs of two mutually orthogonal flat mirrors with $400{\mu}m4 (length) $\times400{\mu}m$ (height) $\times30{\mu}m$ (thickness). The cross angles and surface roughness of the orthogonal vertical mirror were orthogonal, almost $90^{\circ}$ and 3.523 nm rms, respectively. The proposed CCR was completed by combining the orthogonal vertical and horizontal actuated mirrors. Data transmission and modulation at a frequency of 10 Hz was successfully demonstrated using the fabricated CCR at a distance of approximately 50 cm.

• Journal of the Korean Society of Safety
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• v.29 no.4
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• pp.9-14
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• 2014

Self-piercing riveting(SPR) is a mechanical fastening technique which is put pressure on the rivet for joining the sheets. Unlike a spot welding, SPR joining does not make the harmful gas and $CO_2$ and needs less energy consumption. In this study, static and fatigue tests were conducted using tensile-shear specimens with Al-5052 plates for evaluation of fatigue strength of the SPR joints. During SPR joining process for the specimen, using the current sheet thickness and a rivet, the optimal applied punching force was found to be 21 kN. And, the maximum static strength of the specimen produced at the optimal punching force was 3430 N. During the fatigue tests for the specimens, interface failure mode occurred on the top substrate close to the rivet head in the most high-loading range region, but on the bottom substrate close to the rivet tail in the low -loading range region. There was a relationship between applied load amplitude $P_{amp}$ and lifetime of cycle N for the tensile-shear, $P_{amp}=3395.5{\times}N^{-0.078}$. Using the stress-strain curve of the Al-5052 from tensile test, the simulations for fatigue specimens have been carried out using the implicit finite element code ABAQUS. The relation between von-Mises equivalent stress amplitude and number of cycles was found to be ${\sigma}_{eq}=514.7{\times}N^{-0.033}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.984-991
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• 2009

In this study, transonic aeroelastic response analyses have been conducted for the DLR-F4(wing-body) aircraft configuration considering shockwave and flow separation effects. The developed fluid-structure coupled analysis system is applied for aeroelastic computations combining computational structural dynamics(CSD), finite element method(FEM) and computational fluid dynamics(CFD) in the time domain. It can give very accurate and useful engineering data on the structural dynamic design of advanced flight vehicles. For the nonlinear unsteady aerodynamics in high transonic flow region, Navier-Stokes equations using the structured grid system have been applied to wing-body configurations. In transonic flight region, the characteristics of static and dynamic aeroelastic responses have been investigated for a typical wing-body configuration model. Also, it is typically shown that the current computation approach can yield realistic and practical results for aircraft design and test engineers.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1185-1186
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• 2007

The UTM-01 developed in 1998 was the first maglev vehicle in Korea for the urban transit maglev (UTM) system. Through the improvement of UTM-01 and development of UTM02, the commercialization of the UTM system is being prepared now. In order to prepare for the commercialization of maglev, it is necessary that an optimal design of the levitation magnet should be provided for the safe operation of the vehicle. The levitation force is formed through the function of magnetic flux density on the top of magnet poles and gap between magnet pole and guide rail. To generate a magnetic field that is high enough to levitate the vehicle, ferromagnetic materials, such as pure iron for magnet pole and SS400 for guide rail, were used. The heat generated by $I^2R$ loss of magnet conductor makes the thermal convection on the surface of magnet including coil and poles. As these two characteristics are nonlinear phenomena, this paper deals with the nonlinear analysis on the magnetic and thermal properties of the U-type levitation magnet by using 3-D finite element method (FEM). Base on the analysis results, a small scale U-type magnet was designed, manufactured, and tested and it was verified that the magnet manufactured was satisfactory to all the design specifications.