• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.713-720
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• 2015

The sizes of the final blades of a low-pressure (LP) steam turbine have been getting larger for the development of high-capacity power plants. They are also larger than the other blades in the same system. As a result, fatigue damage is caused by a large centrifugal force and a low natural frequency of the blade. Recently, many failure cases have been reported due to repeated turbine startups and their prolonged use. In this study, the causes and mechanism of failure of a LP turbine blade were analyzed by using a finite element method to calculate the centrifugal force, the natural frequency of a stress-stiffening effect, and the harmonic response. It was observed that the expected fatigue damage position matched the real crack position at the airfoil's leading edge, and an equivalence fatigue limit approached a notch fatigue limit.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.905-910
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• 2013

The flow analysis has been made by applying the turbulent models in the helically coiled tubes of heat transfer. The k-${\varepsilon}$ and Spalart-Allmaras turbulent models are used in which the structured grid is applied for the simulation. The velocity vector, the pressure contour, the change of residuals along the iteration number and the friction factors are simulated by solving the Navier-Stokes equations to make clear the Reynolds number effect. The helical tube increases the centrifugal forces by which the wall shear stress become larger on the outer side of the tube. The centrifugal force makes the heat transfer rate locally larger due to the increase of the flow energy, which finds out the close relationship between the pressure drop and friction factor in the internal flow. The present numerical results are compared with others, for example, in the value of friction factor for validation.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.70.4-70.4
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• 2019

Complex organic molecules (COMs) are increasingly observed in the environs of young stellar objects (YSOs), including hot cores/corinos around high-mass/low-mass protostars and protoplanetary disks. It is widely believed that COMs are first formed in the ice mantle of dust grains and subsequently released to the gas by thermal sublimation at high temperatures (T>100 K) in strong stellar radiation fields. In this paper, we report a new mechanism that can desorb COMs from icy grain mantles at low temperatures (T<100K), which is termed rotational desorption. The rotational desorption process of COMs comprises two stages: (1) ice mantles on suprathermally rotating grains spun-up by radiative torques (RATs) are first disrupted into small fragments by centrifugal stress, and (2) COMs and water ice then evaporate rapidly from the tiny fragments (i.e., radius a <1nm) due to thermal spikes or enhanced thermal sublimation due to increased grain temperature for larger fragments (a>1 nm). We discuss the implications of rotational desorption for releasing COMs and water ice in the inner region of protostellar envelopes (hot cores and corinos), photodissociation regions, and protoplanetary disks (PPDs). In shocked regions of stellar outflows, we find that nanoparticles can be spun-up to suprathermal rotation due to supersonic drift of neutral gas, such that centrifugal force can be sufficient to directly eject some molecules from the grain surface, provided that nanoparticles are made of strong material. Finally, we find that large aggregates (a~ 1-100 micron) exposed to strong stellar radiations can be disrupted into individual icy grains via RAdiative Torque Disruption (RATD) mechanism, which is followed by rotational desorption of ice mantles and evaporation of COMs. In the RATD picture, we expect some correlation between the enhancement of COMs and the depletion of large dust grains in not very dense regions of YSOs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.599-606
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• 2010

This paper presents dynamic analysis of FCEV (Fuel Cell Electric Vehicle) Turbo Blower. To analyze the dynamic characteristics of Turbo Blower, finite element model which consists of solid elements is constructed. Evaluation of stress for safety of rotor sleeve due to centrifugal force, Shrink fit analysis in maximum rotation speed is performed. Rotor dynamic analysis of Turbo blower is conducted using Campbell diagram and FEA (Finite element analysis) results are compared with experimental results to evaluate of validity of finite element model. To evaluate of Structure vibration characteristics, Modal analysis and forced vibration analysis are performed through FEA and experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.2
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• pp.206-214
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• 2003

Mean flow and turbulence properties of developing turbulent flows in a 90 degree square bend with spanwise rotation were measured by a hot-wire anemometer. A slanted wire is rotated into 6 orientations and the voltage outputs from them are combined to obtain the mean velocity and Reynolds stress components. The combinative effects of the centrifugal and Coriolis forces due to the curvature and the rotation of bend on the mean motion and turbulence structures are investigated experimentally. Results show that the two body forces can either enhance or counteract each other depending on the flow direction in the bend.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1043-1044
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• 2011

This paper discusses the electromagnetic and mechanical design considerations to improve the design accuracy and power to mass ratio of multi-stack axial flux permanent magnet synchronous generator (AFPMSG). Design accuracy of multi-stack AFPMSG for direct drive wind turbine application is improved by considering magnetic flux leakages and fringing effect. FEM structural analysis is utilized to increase power to mass ratio of three-stack AFPMSG by reducing the rotor yoke thickness considering magnetic and centrifugal forces and Von Mises stress distribution.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.330-337
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• 1995

For a rotating body with cracks, the new energy release rate equation is presented. The derived equation is different from the other researcher's results. It is a path-independent integral which excluded the derivatives of displacements near the crack tip, thereby improving the numerical accuracy of the energy release rate computation. Moreover, as the equation was derived on basis of the energy principle and non-linear elasticity without assumptions, it can applied to the cracked body with arbitrary shape under elastic-plastic deformation. Several examples are treated to demonstrate the efficiency and accuracy of the proposed method compared to existing methods.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.163-169
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• 2003

The vertical roller mill is the important machine grinding and mixing various crude materials in the manufacturing process of portland cement. Table liner is one of grinding elements of vertical roller mill and is subjected to the cyclic bending stress by rollers load and the centrifugal force by rotation of table. It demands $4{\times}10^7$ cycle but has $4{\times}10^6{\sim}8{\times}10^6$ cycle. It fractures at the edge of grinding path of outside roller. The repair expense for it amounts to 30% of total maintenance of vertical roller mill. Therefore, this study shows the fracture mechanism of table liner for vertical roller mill using HDM and fatigue analysis

• Journal of Power System Engineering
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• v.14 no.2
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• pp.65-70
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• 2010

Retaining rings are used to support the field winding end turns from the centrifugal force by the high speed of the field and these are the overstressed parts among the generator parts. There have been several retaining failures in Europe and America, all attributable to stress corrosion cracking in 18Mn-5Cr steel. Since then, each manufacture companies have developed a good 18Mn-5Cr steel in temperature, strength characteristic and it is used in many field now. From many findings and test results, we could conformed that the failure might be grown in the overstressed condition unrelated to the moisture particle.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.3
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• pp.225-230
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• 2008

Reactor starting method has the advantage of simplicity and closed transition in spite of lower starting torque per kVA. This method allows a smooth start with almost no observable disturbance on transition and is suitable for applications such as centrifugal pumps or fans. Reactive power doesn't contribute to work but needs to sustain the electromagnetic field required for the induction motor to operate. Starting power factor of induction motor is specially lower than running power factor. Power factor application is needed to compensate for the lower power factor of induction motor. This power factor compensation systems is occasionally being hit by the effects of the starting reactor connection position at the starting, stopping of high-voltage induction motor. This paper describes voltage and current stress affected by the installation position of power factor compensation application at the reactor starting method.