• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.380-386
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• 2002

Damage behaviors induced in silicon carbide by an impact of particle having different material and size were investigated. Especially, the influence of the impact velocity of particle on the cone crack shape developed was mainly discussed. The damage induced by spherical impact was different depending on the material and size of particles. Ring cracks on the surface of specimen were multiplied by increasing the impact velocity of particle. The steel particle impact produced larger ring cracks than that of SiC particle. In the case of high velocity impact of SiC particle, radial cracks were produced due to the inelastic deformation at the impact site. In the case of the larger particle impact, the damage morphology developed was similar to the case of smaller particle one, but a percussion cone was farmed from the back surface of specimen when the impact velocity exceeded a critical value. The zenithal angle of cone cracks developed into SiC material decreased monotonically with increasing of the particle impact velocity. The size and material of particle influenced more or less on the extent of cone crack shape. An empirical equation, $\theta$= $\theta$$\sub$st/, v$\sub$p/(90-$\theta$$\sub$st/)/500 R$\^$0.3/($\rho$$_1$/$\rho$$_2$)$\^$$\frac{1}{2}$/, was obtained as a function of impact velocity of the particle, based on the quasi-static zenithal angle of cone crack. It is expected that the empirical equation will be helpful to the computational simulation of residual strength in ceramic components damaged by the particle impact.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.4
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• pp.102-106
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• 2000

We report scanning force microscope (SFM) observations of enhanced calcite dissolution in aqueous solution due to mechanical stimulation induced by the SFM tip. Images and mechanical treatment were performed in saturated ($\geq$ 60 ${\mu}{\textrm}{m}$) CaCO$_3$ solution adjusted to pH~9. Small area scans of monolayer steps significantly increased the step velocity in the scanned area (in the direction corresponding to dissolution) when the applied contact force is above about 160 nN fer the tips employed. The step velocity could be increased at least an order of magnitude by scanning at even higher contact forces (e.g.,270nN). This enhancement is a function of step orientation relative to the calcite lattice. Indentations near preexisting steps also locally enhance the step velocity. We present evidence that the higher dissolution rates are caused by stress-induced increases in the rate of double-kink nucleation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.365-370
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• 2004

Simultaneous measurement with PLIF(Planar Laser-Induced Fluorescence) and Stereo-PIV(Stereo Particle Image Velocimetry) was performed to investigate the structural characteristics of flow field in Rushton Turbine Mixer. Instantaneous 3D velocity fields are measured by two 2K${\times}$2K CCD cameras focused on an object plane with the angular displacement methods while the concentration fields are obtained through the measurement of the fluorescence intensity of Rhodamine B tracer excited by the second pulse of Nd:Yag laser light. Image distortion due to the camera view-angle is compensated by a mapping function. Finally, the spatial structures of turbulent flow around Rushton turbine were identified by the calculation of synchronized data of the velocity field and concentration field.

• Smart Structures and Systems
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• v.22 no.1
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• pp.95-103
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• 2018

Active vibration control via inertial mass actuators has been shown as an effective tool to significantly reduce human-induced vertical vibrations, allowing structures to satisfy vibration serviceability limits. However, a lot of practical obstacles have to be solved before experimental implementations. This has motivated simple control techniques, such as direct velocity feedback control (DVFC), which is implemented in practice by integrating the signal of an accelerometer with a band-pass filter working as a lossy integrator. This work provides practical guidelines for the tuning of DVFC considering the damping performance, inertial mass actuator limitations, such as stroke and force saturation, as well as the stability margins of the closed-loop system. Experimental results on a full scale steel-concrete composite structure (behaves similar to a footbridge) with adjustable span are reported to illustrate the main conclusions of this work.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.24-30
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• 1985

An experimental work to predict critical flow velocity to give whirling instability on staggered array tube banks model which is located in wind tunnel is presented. The critical flow velocity was obtained by measuring flow induced tube vibration on three tube array models having different pitch to diameter ratio as changing damping ratio and natural frequency of tube model. The obtained experimental results are directly compared with the numbers of other investigators and partly proved the truth of Blevin's new idea to predict critical flow velocity.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.694-699
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• 2003

Simultaneous measurement with PLIF(Planar Laser-Induced Fluorescence) and Stereo-PIV(Stereoscopic Particle Image Velocimetry) was performed to investigate the structural characteristics of flow field in Rushton Turbine Mixer. Instantaneous 3D velocity fields are measured by two 2K ${\times}$ 2K CCD cameras focused on an object plane with the angular displacement methods while the concentration fields are obtained through the measurement of the fluorescence intensity of Rhodamine B tracer excited by the second pulse of Nd:Yag laser light. Image distortion due to the camera view-angle is compensated by a mapping function. Finally, the spatial structures of turbulent mixing around Rushton turbine were identified by the calculation of cross-correlation fields between the velocity and concentration field.

• Bulletin of the Society of Naval Architects of Korea
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• v.21 no.3
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• pp.19-26
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• 1984

Guilloton's wedge method is extended to evaluated velocity components on and around a ship hull. A ship is divided into a number of layers each of which is approximated by the superposition of so many wedges. These wedges start from the stations evenly placed along the length of the ship. The Michell potential is used to obtain the field generating properties of a wedge. The derivatives of this potential represent then the velocity components induced by the wedge. Superposition of velocities induced at a fixed field point by all the wedges placed at the appropriate positions to approximate the hull will result in the velocity associated with the ship at a particular speed.

• Journal of Industrial Technology
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• v.27 no.B
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• pp.29-36
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• 2007

A comparative study of airborne salinity and sea wind was done for a coastal area, Sokcho city, of East Sea in Kangwon province, Korea. In this study, a relationship between the formation of airborne salinity and wind velocity was investigated, and then the airborne salinity was simulated and forecasted by the obtained wind-salinity characteristics. It is founded that most airborne salinity is brought by sea winds with the occurrence of velocity, higher than and equal to 4m/s, while the occurrence of lower wind velocities (ie., lower than 4m/s) in sea wind and the occurrence of inland wind give diluted effects on the airborne transfer. By using these characteristics and a proposed linear equation model, the salinity in Sokcho city is successfully simulated and forecasted. It is expected that the linear equation model may be useful for durability design of concrete structures under the conditions of chloride attack, induced by the airborne salinity.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.498-506
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• 2007

Using wind tunnel, experimental approaches were employed to investigate fluidelastic instability of tube bundles, subjected to uniform cross flow. There are several flow-induced vibration excitation mechanisms, such as fluidelastic instability, periodic wake shedding resonance, turbulence-induced excitation and acoustic resonance, which could cause excessive vibration in shell-and tube heat exchanges. Fluidelastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to cross flow. The system comprised of cantilevered flexible cylinder(s) and rigid cylinders of normal square array, In order to see the characteristics of flow in tube bundles, particle image velocimetry was used. From a practical design point of view, Fluidelastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping. The threshold flow velocity for dynamic instability of cylinder rows is evaluated and the data for design guideline is proposed for the tube bundles of normal square array.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1650-1657
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• 2019

Fluidelastic instability and nonlinear dynamics of tube bundles is a key issue in a steam generator. Especially, once the post-instability motion of the tube becomes larger than the clearance gap to other tubes, effective contact or impact between the tubes under consideration and the other tube inevitable. There is seldom theoretical analysis to the nonlinear dynamic characteristics of a tube array in two-phase flow. In this paper, experimental and numerical studies were utilized to obtain the critical velocity of the flow-induced instability of a rotated triangular tube array. The calculation results agreed well with the experimental data. To explore the post-instability dynamics of the tube array system, a Runge-Kutta scheme was used to solve the nonlinear governing equations of tube motion. The numerical results indicated that, when the flow pitch velocity is larger than the critical velocity, the tube array system is undergoing a limit cycle motion, and the dynamic characteristics of the tube array are almost similar for different void fractions.