• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.299-306
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• 2001

Crushed Stone Pile(CSP) is one of the ground improvement methods available to loose sand and clayey ground by forming compacted CSP in the weak soil layer. The effects of this method are enhancement of ground bearing capacity, reduction of settlement and prevention of lateral ground movement in cohesive layer, reduction of liquefaction potential in sandy ground. This study performs model tests in 1.0m${\times}$1.0m${\times}$1.0m and 1.5m${\times}$1.5m${\times}$l.2m model tank to observe bearing capacity of CSP treated ground. The area replacement ratio of CSP composite ground varies 20%, 30% and 40% with square grid pattern. After the composite ground was consolidated under pressure of 0.5kg/$\textrm{cm}^2$ and 1.0kg/$\textrm{cm}^2$, load tests were carried out. The results show that ultimate bearing capacity increases with area replacement ratio and the preconsolidation pressure of ground.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.476-481
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• 1999

This paper describes a new technique for measurement of the displacement less than one-quarter of the wavelength of ultrasonic wave using ultrasonic pulse-echo method. The technique determines the displacement of a journal bearing from the amplitudes of the total reflected waves from the surface of journal inside the bearing. Vibration of journal bearing can be measured without using a very high frequency ultrasonic transduce over 100MHz which must be used in the conventional techniques for the precision measurement of a small displacement. The method also requires no inversion process to extract the thickness from the waveforms of the reflected waves, so that it makes possible on-line measurement of the vibration of journal bearing.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.425-431
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• 1999

Nowadays development of electric and optical devices needs precision more and more. This study focuses on hydrostatic journal bearing of grinding wheel spindle. It presents theoretical analysis about cylinder type self-controlled restrictor to control flux of oil flowing into pockets around the hydrostatic journal bearing. As a result of this analysis, optimal properties to maximize bearing stiffness such as initial cross distance, supply pressure, diameter of two supply holes, pre-load of spring and clearance between spindle and housing can be obtained. Therefore, by using them it is possible to estimate bearing stiffness and the performance of grinding wheel spindle can be improved.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.136-145
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• 1999

This paper describes the surface roughness effect in parallel thrust bearing. In mixed lubrication, some contacts will take place between asperities, and partial lubrication will occur. An average Reynolds Equation is utilized to determine effects of surface roughness on partially lubricated contacts. By using an autocorrelation function for the surface profile, surface model is generated numerically Although the two surfaces are parallel in thrust bearing separated by thin film, the pressure peak is formed due to asperites. By means of surface profile parameters, it is shown that which surface is optimal for the parallel thrust bearing.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1043-1048
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• 2002

This paper considers the vibration problem of vehicle driveline which consists of two propeller shafts and the center bearing. The excessive vibration occurs at the center bearing when the vehicle starts to run. Using the kinematic constraints at the universal joint between two propeller shafts, we develop an one d.o.f model which describes the radial motion of the center bearing. We find out the vibration occurs at the specific vehicle speed corresponding to the natural frequency of the model. Comparing the simulation results with test results we also show that the vibration at low vehicle speed is caused primarily by the joint angle and secondarily by the mis-aligned yoke flange rather than by the unbalance.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.237-242
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• 2001

In this paper, we theoretically analyzed the NRRO(the non-repeatable run-out) of a ball bearing with ball geometric imperfection. The quasi-static and dynamic analysis of a ball bearing was performed to calculate the displacement of shaft center caused by the ball form errors while the shaft is rotating. From consideration of the generating mechanism of NRRO, it is found that the size and form errors of ball generate vibrations with (equation omitted)$\_$c/ and n(equation omitted)$\_$b/${\pm}$(equation omitted)$\_$c/(where n is even) components, respectively. The ball form errors of a ball bearing were precisely measured and NRRO of a ball bearing was calculated using the measured data. A statistical approach was peformed to analyze NRRO of ball bearings with radial errors.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.84-89
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• 2014

Data-driven method for fault diagnostics system often use machine learning technique. To use such technique proper signal processing should be implemented such as time synchronous averaging (TSA) for ball bearing systems. However, for journal bearing diagnostics systems not much has been researched, and yet a proper signal processing method has not been studied. Therefore, in this research an optimal datum unit for a reliable journal bearing diagnostics system along with angular resampling process is being suggested. Before extracting time and frequency domain features, angular resampling is applied to each cycle of vibration data. As to preserve the characteristics of vibration signal, averaging method is replaced by finding the optimal datum unit which strengthens statistical characteristics of vibration signal. Then 20 features were extracted for various cases, and those features are being evaluated by two criteria, separability and classification accuracy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.768-770
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• 2014

A shaft of a reciprocating compressor receives bending force by piston, which makes movement of the shaft. The movement of the shaft affects durability and becomes a source of noise. In this paper, a cylinder is modeled by considering motion of a suction and discharge valve. The journal bearing is modeled by Bernoulli's equation. The trajectory of shaft which is considered cylinder and journal bearing can be calculated by finite element method. It will help a design of shaft to increase durability and reduce noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.97-98
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• 2014

Vibration signal has been widely utilized in the diagnostics of rotating mechanical system. Diagnostics systems in rotating machinery are depends on the vibration data which are acquired from the system. However, the characteristics of acquired data can be vary according to the position of anomaly installed or the position of data acquired. In this research, the coordinate transform of journal bearing vibration signal was proposed to overcome the limitation mentioned above. Journal bearing systems are equipped two gap sensors with ninety degree angles, and it can enable to generate coordinate transformed signals in arbitrary angle domain. More abundant information for each normal or anomaly conditions are obtained from coordinate transformation than only the data of the existing measuring position, then we have developed a reliable and robust diagnosis algorithm for journal bearing system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.888-891
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• 2002

This paper presents the lubrication characteristics of a disk type wavy thrust bearing. The hydrodynamic pressure distributions in the fluid film are numerically solved the Reynolds equation and then the bearing load capacity and friction forces acting on the disk are calculated. Especially the effects of number and amplitude of the circumferential waves are investigated for tilted operating conditions. The results showed that the load capacity increases with wave amplitude and optimum wave number exists for given design conditions. Therefore the results can be applied to enhance the lubrication performance of thrust bearing adopted in the scroll compressor.