• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.134-141
• /
• 2008

To evaluate the engineering properties of soil, the laboratory test always is carried out using samples obtained from the field. There are many studies to estimate the effect of sampling disturbance. The objective of this study appraises the disturbance using the shear wave velocity. The new shelby tube which three transducers are installed every 20cm interval is used. To laboratory tests, the large-scale consolidometer (calibration chamber) is used. During 1cm penetration, the shear wave velocity is measured by every transducer. The initial sampling disturbance is assessed through the velocity difference from bottom to right upside transducer. After finishing the sampling, the velocity is still measured every time to assess the soil disturbance in shelby tube itself. Through the measured velocity, the effect of disturbance is appraised. This study suggests that the sampling disturbance of shelby tube is effectively evaluated using shear wave velocity.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.4
• /
• pp.708-716
• /
• 1989

The purpose of this study is to investigate the breakup mechanism of a liquid jet in a coaxial air flow. By using the high speed camera, measured were the instantaneous change of the wave length, amuplitude of disturbance, propagation velocity of wave and breakup length, and the relationships between those data were examined. The shape of the surface of the liquid jet appeared to be rather complicated and irregular. The growth rate of disturbance was not constant, and was changed at the moment of 3ms prior to the disintegration of the liquid jet. Simultaneously at this moment, the propagation velocities of the sequential waves were reversed and the wave length was rapidly decreased.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.6
• /
• pp.766-772
• /
• 2003

The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.1
• /
• pp.70-86
• /
• 2015

Short crested waves play an important role for planning and design of harbours. In this context a numerical simulation is carried out to evaluate wave tranquility inside a real harbour located in east coast of India. The annual offshore wave climate proximity to harbour site is established using Wave Model (WAM) hindcast wave data. The deep water waves are transformed to harbour front using a Near Shore spectral Wave model (NSW). A directional analysis is carried out to determine the probable incident wave directions towards the harbour. Most critical threshold wave height and wave period is chosen for normal operating conditions using exceedence probability analysis. Irregular random waves from various directions are generated confirming to Pierson Moskowitz spectrum at 20m water depth. Wave incident into inner harbor through harbor entrance is performed using Boussinesq Wave model (BW). Wave disturbance experienced inside the harbour and at various berths are analysed. The paper discusses the progresses took place in short wave modeling and it demonstrates application of wave climate for the evaluation of harbor tranquility using various types of wave models.

• Journal of Mechanical Science and Technology
• /
• v.17 no.9
• /
• pp.1388-1396
• /
• 2003

The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. The instability labeled Type II by Faller occurs first at lower Reynolds number than that of well known Type I instability. Detailed numerical values of the amplification rates, neutral curves and other characteristics of the two instabilities have been calculated over a wide range of parameters. Presented are the neutral stability results concerning the two instability modes by solving the appropriate linear stability equations reformulated not only by considering whole convective terms but also by correcting some errors in the previous stability equations. The present stability results agree with the previously known ones within reasonable limit. Consequently, the flow is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.75. Some spatial amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$ = 12.5$^{\circ}$ to 15$^{\circ}$. Also, some temporal amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$= 12$^{\circ}$ to 15$^{\circ}$. The flow instability was observed by using a white titanium tetrachloride gas over rotating disk system. When the numerical results are compared to the present experimental data, the numerical results agree quantitatively, indicating the existence of the selective frequency mechanism.

• Journal of Institute of Control, Robotics and Systems
• /
• v.3 no.1
• /
• pp.40-45
• /
• 1997

A robust disturbance rejection controller for the hovering motion of underwater vehicles in near the surface of sea is presented. The suggested controller consists of two control parts, the one is disturbance observer for taking into account the effects of sea wave and missile-launching forces, and the other is sliding mode controller for the robust stability of underwater vehicles with model uncertainties and nonlinearities. It is shown that the sliding mode control system with disturbance observer is more effective compared with the sliding mode control system, especially in case that large sea wave force is affected.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.4
• /
• pp.415-423
• /
• 2003

The hydrodynamic instability of the three-dimensional boundary-layer over a rotating disk has been numerically investigated for these flows; Ro = -1, -0.5, and 0, using linear stability theory. Detailed numerical values of the disturbance wave number. wave frequency. azimuth angle. radius (Reynolds number, Re) and other characteristics have been calculated for the pre-swirl flows. On the basis of Ekman and Karman boundary layer theory, the instability of the pre-swirl flows have been investigated for the unstable criteria. The disturbance will be relatively fast amplified at small fe and within wide bands of wave number compared with previously known Karman boundary-layer results. The flow (Ro =-0.5) is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.9. It has a larger range of unstable interval than Karman boundary layer and can be unstable at smaller Re.

• Journal of Mechanical Science and Technology
• /
• v.14 no.3
• /
• pp.358-368
• /
• 2000

The hydrodynamic stability of the Karman boundary-layer flow due to a rotating disk has been numerically investigated for moving disturbance waves. The disturbed flow over a rotating disk can lead to transition at much lower Re than that of the well-known Type I instability mode. This early transition is due to the excitation of the Type II instability mode of moving disturbances. Presented are the neutral stability results concerning the two instability modes by solving new linear stability equations reformulated not only by considering whole convective terms but by correcting some errors in the previous stability equations. The reformulated stability equations are slightly different with the previous ones. However, the present neutral stability results are considerably different with the previously known ones. It is found that the flow is always stable for a disturbance whose dimensionless wave number k is greater than 0.75.

• 정보저장시스템학회:학술대회논문집
• /
• 2005.10a
• /
• pp.242-245
• /
• 2005

The rotating flow in the space between co-rotating disks is of considerable importance in information storage systems. Hard disk drivers(HDD) in computer are used extensively as data storage capacity. The trend in the computer industry to produce smaller disk drives rotating at higher speed requires an improved understanding of fluid motion in the space between disks. In this study, we have tried LES model for inner-disk flowfield to investigate the flow disturbance and the flow structure driven by co-rotating disks. The boundary pattern between inner region and outer region obtained lobe-shape structure clearly and its number has been validated on experimental data by our previous study. We obtain the spectra of velocity and pressure components with several frequencies. We revealed there are two kinds of disturbances, one is global wave propagation and another is local wave propagation on Ekman boundary layer.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.67 no.11
• /
• pp.1555-1561
• /
• 2018

Tracking and detecting targets by the millimeter wave seeker is affected by movement of platform. Stabilization equipments use an inertial sensor to compensate for disturbance of stabilizing gimbal or platform. In the direct line of sight stabilization system, an inertial sensor is mounted on inner gimbal to compensate the disturbance directly, so the performance is excellent and the implementation method is simple. However gimbal design requires somewhat larger volume. Since an inertial sensor is mounted on gimbal base in the indirect line of sight stabilization system, additional space of gimbal is not required for the gimbal design. However, this method does not directly compensate for the disturbance of the line of sight stabilization axis, which can degrade performance. In order to perform the tracking performance, two methods are analyzed for line of sight stabilization performance based on direct and indirect of a 2-axis gimbaled servo system for millimeter wave seeker in this study. The simulation and experimental results validate the performance comparison of two methods.