• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.3
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• pp.388-397
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• 1999

Numerical simulations are carried out for the magnetic Czochralski single crystal growth system. It Is shown that a magnetic field significantly suppresses the convective flow and as the strength of magnetic field becomes to be stronger, the heat transfer in the melt is dominated by conduction rather than convection. By imposing a cusp magnetic field, the growth interface shape becomes convex toward the melt. When the axial magnetic field is imposed, there occurs an inversion of the interface shape with increase of the magnetic field strength. The oxygen concentration near the interface decreases with increasing cusp magnetic field strength while axial field causes an increase of an oxygen concentration at the central region and decrease of that at the edge of the crystal. The results show that the cusp magnetic field has advantages over an axial magnetic field In the radial uniformity of oxygen as well as in the additional degree of control.

• Architectural research
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• v.2 no.1
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• pp.55-60
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• 2000

Recently, there is a great demand for precast reinforced concrete (RC) construction methods on the purpose of simplicity in construction. Nishimatsu Construction Company has developed a construction method with precast reinforced concrete members in medium-rise building. In this construction method, how to joint precast members, especially the anchorage of the main bar of beam, is important problem. In this study, the structural performance of exterior joints with precast members was investigated. The parameters of the test specimens are anchorage type of the main bar of beam (U-shape anchorage or anchorage plate) and the ratio of the column axial force to the column strength. Specimens J-3 and J-4 used U-shape anchorage and the ratio of the column axial force of specimen J-4 was higher. On the other hand, specimens J-5 and J-6 used anchorage plate, and the anchorage lengths are 15d and 18d, respectively. Experimental results are summarized as follows; 1) For the joints with beam flexural failure mode, it was found that the maximum strength of specimen with anchorage plate is equal to or larger than that of specimen with conventional U-shaped anchorage if the anchorage length of more than 15d would be ensured, 2) Each specimen shows stable hysteretic curves and there were no notable effects on the hysteretic characteristics and the maximum strength caused by the anchorage method of beam main bar and the difference of column axial stress level.

• International Journal of Fluid Machinery and Systems
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• v.6 no.1
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• pp.25-32
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• 2013

Data centers have been built with spread of cloud computing. Further, electric power consumption of it is growing rapidly. High power cooling small-sized fans; high pressure and large flow rate small-sized fan, are used for servers in the data centers and there is a strong demand to increase power of it because of increase of quantity of heat from the servers. Contra-rotating rotors have been adopted for some of high power cooling fans to meet the demand for high power. There is a limitation of space for servers and geometrical restriction for cooling fans because spokes to support fan motors, electrical power cables and so on should be installed in the cooling fans. It is important to clarify complicated internal flow condition and influence of a geometric shape of the cooling fans on performance to achieve high performance of the cooling fans. In the present paper, the performance and the flow condition of the high power contra-rotating small-sized axial fan with a 40mm square casing are shown by experimental and numerical results. Furthermore, influence of the geometrical shape of the small-sized cooling fan on the internal flow condition is clarified and design guideline to improve the performance is discussed.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.655-663
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• 2005

Tribological characteristics in the sliding parts of oil hydraulic piston pumps are very important in increasing overall efficiency. In this study, the fluid film between the valve plate and the cylinder block was measured by using a gap sensor and the mercury-cell slip ring unit under real working conditions. To investigate the effect of the valve shape, we designed three valve plates each having a different shape. One of the valve plates was without bearing pad, another valve plate had bearing pad and the last valve plate was a spherical valve plate. It was noted that these three valve plates observed different aspects of the fluid film characteristics between the cylinder block and the valve plate. The leakage flow rates and the shaft torque were also investigated in order to clarify the performance difference between these three types of valve plates. From the results of this study, we found that the spherical valve plate estimated good fluid film patterns and good performance more than the other valve plates in oil hydraulic axial piston pumps.

• New & Renewable Energy
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• v.8 no.2
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• pp.44-51
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• 2012

The aim of this paper is to examine the hydraulically optimized camber of a blade. Prior studies have tried to determine the sound method of design on small-hydro turbines. These have appeared to realize a reasonably efficient small-hydro turbine. Nonetheless, specific and accurate design data have not as yet been established for the shape of the runner blade. Hence, this study examines the performance characteristic of an axial propeller turbine with 0~8% camber variations. The results of output power, efficiency, and pressure distribution of the turbine are graphically depicted. The definition of camber refers to the NACA airfoil. The commercial finite element analysis (FEA) packages, ANSYS, and CFX are used in this study. The results revealed the performance characteristics on small-hydro turbine and suggested a highly efficient section shape of the runner.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.91-96
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• 2010

The combination of a bolt and nut is the element most widely used for connecting machines and structures. When a load is repetitively applied in the direction right angle to the bolt axis after the bolt and nut is fastened, the nut gradually becomes loose. To solve this problem, in this study, a new type of the loose-proof nut, called a lock nut, is developed. The lock nut is equipped with a spring, and the spring increases the axial force of the bolt. Then, the connection force between the bolt and nut is also augmented. Three dimensional finite element models for the bolt and spring are generated, and the change of the axial force of the bolt while the bolt is being inserted into the spring is analyzed using MSC/Marc, a commercial finite element program. Finally, the optimum shape of the spring is found according to the response surface analysis methodology. The optimization result is verified by comparing the variation of the axial force of the bolt when the bolt is inserted to the initial and optimized spring.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.195-203
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• 2008

This paper aims to evaluate the yield stress of SM570TMC concrete-filed H-shape steel columns subjected to axial force. These columns were evaluated and compared using quasi-static tests. The displacements and the axial loads column specimens were measured during the tests, and test results showed that the yield stress of concrete-filed H-shape steel columns subjected to axial load could be predicted using the previously proposed yield stress of steel columns.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.397-400
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• 2011

MDO Optimization for a low pressure axial compressor rotor has been carried out to improve aerodynamic performance and structural stability. Global optimized solution was obtained from an artificial neural network model with genetic algorithm. Optimized rotor model has a high blade loading near hub and near zero incidence flow angle near tip region to reduce the incidence loss and flow separation at trailing edge region. Also the rotor shape is converged to a trapezoid shape to reduce the maximum stress occurred at the root of the blade. Numerical simulation results show that rotor has 87.6% rotor efficiency and safety factor over than 3.

• Structural Engineering and Mechanics
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• v.35 no.4
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• pp.387-407
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• 2010

In this paper, using perturbation and Galerkin method, the response of a resonant viscoelastic microbeam to an electric actuation is obtained. The microbeam is under axial load and electrical load. It is assumed that midplane is stretched, when the beam is deflected. The equation of motion is derived using the Newton's second law. The viscoelastic model is taken to be the Kelvin-Voigt model. In the first section, the static deflection is obtained using the Galerkin method. Exact linear symmetric mode shape of a straight beam and its deflection function under constant transverse load are used as admissible functions. So, an analytical expression that describes the static deflection at all points is obtained. Comparing the result with previous research show that using deflection function as admissible function decreases the computation errors and previous calculations volume. In the second section, the response of a microbeam resonator system under primary and secondary resonance excitation has been obtained by analytical multiple scale perturbation method combined with the Galerkin method. It is shown, that a small amount of viscoelastic damping has an important effect and causes to decrease the maximum amplitude of response, and to shift the resonance frequency. Also, it shown, that an increase of the DC voltage, ratio of the air gap to the microbeam thickness, tensile axial load, would increase the effect of viscoelastic damping, and an increase of the compressive axial load would decrease the effect of viscoelastic damping.

• Steel and Composite Structures
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• v.32 no.3
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• pp.373-388
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• 2019

This study proposes a new concept of an axial damper using the combination of shape memory alloy (SMA), friction devices, and polyurethane springs. Although there are many kinds of dampers to limit the damages, large residual deformation may happen and it causes much repairing cost for restoring the structure to the initial position. Also in some of the dampers, a special technology for assembling and fabricating is needed. One of the most important advantages of this damper is the ability to remove all the residual deformation using SMA plates and simple assembling without any special technology to fabricate. In this paper, four different dampers (in presence or omission of friction devices and polyurethane springs) are investigated. All four cases are analyzed in ABAQUS platform under cyclic loadings. In addition, the SMA plates are replaced by steel ones in four cases, and the results are compared to the SMA dampers. The results show that the axial polyurethane friction (APF) damper could decrease the residual deformation effectively. Also, the damper capacity and dissipated energy could be improved. The analysis showed that APF damper is a good recentering damper with a large amount of energy dissipation and capacity, among others.