• Tribology and Lubricants
• /
• v.35 no.3
• /
• pp.190-198
• /
• 2019

Gas foil bearings (GFBs) enable small- to medium-sized turbomachinery to operate at ultra-high speeds in a compact design by using ambient air or process gas as a lubricant. When using air or process gas, which have lower viscosity than lubricant oil, the turbomachinery has the advantage of reduced power loss from bearing friction drag. However, GFBs may have high Reynolds number, which causes turbulent flows due to process gas with low viscosity and high density. This paper analyzes gas foil journal bearings (GFJBs) with high Reynolds numbers and studies the effects of turbulent flows on the static and dynamic performance of bearings. For comparison purposes, air and R-134a gas lubricants are applied to the GFJBs. For the air lubricant, turbulence is dominant only at rotor speeds higher than 200 krpm. At those speeds, the journal eccentricity decreases, but the film thickness, power loss, and direct stiffness and damping coefficients increase. On the other hand, the R-134a gas lubricant, which that has much higher density than air, causes dominant turbulence at rotor speeds greater than 10 krpm. The turbulent flow model predicts decreased journal eccentricity but increased film thickness and power loss when compared with the lamina flow model predictions. The vertical direct stiffness and damping coefficients are lower at speeds below 100 krpm, but higher beyond that speeds for the turbulent model. The present results indicate that turbulent flow effects should be considered for accurate performance predictions of GFJBs with high Reynolds number.

• Structural Engineering and Mechanics
• /
• v.86 no.2
• /
• pp.167-180
• /
• 2023

This work applies a four-known quasi-3D shear deformation theory to investigate the bending behavior of a functionally graded plate resting on a viscoelastic foundation and subjected to hygro-thermo-mechanical loading. The theory utilizes a hyperbolic shape function to predict the transverse shear stress, and the transverse stretching effect of the plate is considered. The principle of virtual displacement is applied to obtain the governing differential equations, and the Navier method, which comprises an exponential term, is used to obtain the solution. Novel to the current study, the impact of the viscoelastic foundation model, which includes a time-dependent viscosity parameter in addition to Winkler's and Pasternak parameters, is carefully investigated. Numerical examples are presented to validate the theory. A parametric study is conducted to study the effect of the damping coefficient, the linear and nonlinear loadings, the power-law index, and the plate width-tothickness ratio on the plate bending response. The results show that the presence of the viscoelastic foundation causes an 18% decrease in the plate deflection and about a 10% increase in transverse shear stresses under both linear and nonlinear loading conditions. Additionally, nonlinear loading causes a one-and-a-half times increase in horizontal stresses and a nearly two-times increase in normal transverse stresses compared to linear loading. Based on the article's findings, it can be concluded that the viscosity effect plays a significant role in the bending response of plates in hygrothermal environments. Hence it shall be considered in the design.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.4
• /
• pp.396-403
• /
• 2016

This study is based on the evaluation of a single component injection type adhesive repair material and a new 2 component type used in leakage of underground concrete structures. The studies showed that based on different mix ratio of the 2 component type adhesive sealant comprised of an asphalt main and latex mixture agent the viscosity of the material compound differed significantly. Based on a permeability testing, injection and economic efficiency, and performance, the appropriate ratio was determined to be 6:1 and was proceeded to the KS F 4935 evaluation method. The 2 component type adhesive sealant uses a static mixer and a cartridge type container for the injection procedure and was able to satisfy the evaluation criteria outlined in the KS F 4935 standard.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1018-1023
• /
• 2005

A new MR cylinder with built-in valves using MR fluid (MR valve) is suggested and fabricated for fluid control systems. The MR fluid is a newly developed functional fluid whose obvious viscosity is controlled by the applied magnetic field intensity. The MR cylinder is composed of cylinder with small clearance and piston with electromagnet. The differential pressure is controlled by the applied magnetic field intensity. It has the characteristics of simple, compact and reliable structure. The size of MR cylinder and piston has ${\varphi}30mm{\times}300mm\;and\;{\varphi}28.5mm{\times}120mm$ in face size, respectively and 0.8mm in gap length. Through experiments, it was found that the differential pressure is controlled by the applied magnetic field intensity under little influence of the flow rate, which corresponds to a pressure control valve. The differential pressure of 0.47MPa and contact force of 320N were obtained with the input current of 1.5A. The rising time of force was 1.1s in step response of a manipulator using the MR cylinder. The effectiveness of the MR cylinder was also demonstrated through the force control.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.3
• /
• pp.240-249
• /
• 2008

This paper presents an electromagnetic design method for magneto-rheological (MR) valves. Since the apparent viscosity of MR fluids is adjusted by applying magnetic fields, the MR valves can control high-level fluid power without any mechanical moving parts. In order to improve the performances of the MR valve, it is important that the magnetic field is effectively supplied to the MR fluid. For the purpose, the magnetic circuit composed with the yoke for forming magnetic flux path, the electromagnetic coil and the MR fluid should be well designed. In order to improve the static characteristic of the MR valve, the length of the magnetic flux path is decreased by removing the unnecessary bulk of the yoke. Also, in order to improve its dynamic and hysteretic characteristics, the magnetic reluctance of the magnetic circuit should be increased by minimizing the cross-sectional area of the yoke through which the magnetic flux passes. After two MR valves, one is a conventional type valve and the other is the proposed one, are designed and fabricated, their performances are evaluated experimentally.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.7 s.172
• /
• pp.130-136
• /
• 2005

A new MR cylinder with built-in valves using MR fluid (MR valve) is suggested and fabricated fur fluid control systems. The MR fluid is a newly developed functional fluid whose obvious viscosity is controlled by the applied magnetic field intensity. The MR cylinder is composed of cylinder with small clearance and piston with electromagnet. The differential pressure is controlled by the applied magnetic field intensity. It has the characteristics of simple, compact and reliable structure. The size of MR cylinder and piston has $\varphi30mm\times300mm$ and $\varphi28.5mm\times120mm$ in face size, respectively and 0.8mm in gap length. Through experiments, it was found that the differential pressure is controlled by the applied magnetic field intensity under little influence of the flow rate, which corresponds to a pressure control valve. The differential pressure of 0.47MPa was obtained with the input current of 1.5A. The rising time was 2.3s in step response of a manipulator using the MR cylinder. The effectiveness of the MR cylinder was also demonstrated through the position control.

• Journal of Fashion Business
• /
• v.16 no.1
• /
• pp.41-51
• /
• 2012

Polyester is mainly used as a bedding filler material. PLA fiber as an eco-friendly material for substituting polyester has a low melting temperature and therefore a hardening process is impossible. This study is to develop the oil for feather touch that can treat at the melting temperature of PLA. The slippery and soft aminosilicone emulsion, and the bulky epoxysilicone emulsion were used. They had proper viscosity and particle size for flexibility and elasticity. When using methoxy aminosilane [$H_2NSi(OCH_3)_3$] as an aminosilane and [$Zn(OCOCH_3)_2$] as a catalyst, the hardening reaction was fast and effective. Feather touch process were treated by 2 steps. At first step, aminosilicone emulsion, epoxysilicone emulsion and methylaminosilane were mixed and homogenized, and at second step, 5% blened solution of the first step, Zn catalyst 1%, distilled water 94% were treated at PLA fiber. After treatment the static friction coefficient and dynamic friction coefficient were reduced to 23.5-60.8% and 30.0-61.3% respectively, and the laundry and sun light fastnesses have not shown any decrease.

• Advances in concrete construction
• /
• v.13 no.4
• /
• pp.281-289
• /
• 2022

3D printing cement-based materials (3DPCBM) is an innovative rapid prototyping technology for construction materials. This study is tested on the rheological behavior, printability and buildability of steel slag (SS) content based on the extrusion system of 3D printing. 0, 8 wt%, 16 wt%, 24 wt%, 32 wt% and 40 wt% SS was replaced cement, The test results revealed that the addition of SS would increase the fluidity of the printed paste, prolong the open time and setting time, reduce the plastic viscosity, dynamic yield stress and thixotropy, and is beneficial to improve the pumping and extrudability of 3DPCBM. With the increase of SS content, the static yield stress developed slowly with time which indicated that SS is harmful to the buildability of printing paste. The content of SS in 3DPCBM can reach up to 40% at most under the condition of satisfying rheological property and buildability, it provides a reference for the subsequent introduction of SS and other industrial solid waste into 3DPCBM by explored the influence law of SS on the rheological properties of 3DPCBM.

• Journal of Life Science
• /
• v.19 no.10
• /
• pp.1432-1437
• /
• 2009

The aim of this study is to investigate cane molasses pretreatments for the production of cellulose by Acetobacter sp. V6, which has excellent bacterial cellulose (BC) producing capacity in the shaking culture. Among pretreatments of cane molasses, 1% (w/v) tricalcium phosphate (TP) treatment was more efficient in BC production. The physico-chemical properties of BCs that were produced in static and shaking cultures were also investigated. Although BC had an emulsifying ability, its emulsion stability was low. Water holding capacity (WHC) of BC was high; the WHC of BC produced in static culture was 14 times higher than that of $\alpha$-cellulose. In addition, the viscosity of BC was higher than that of $\alpha$-cellulose. Composition analysis by FT-IR showed no difference in composition between BC and plant cellulose. In the crystallinity analysis by XRD, all BC samples showed crystallinity. All BC samples showed reticulated structures consisting of ultrafine cellulose fibriles. Microfibriles of cellulose from static culture were especially more compact than those of cellulose from shaking culture.

• The Korean Journal of Rheology
• /
• v.10 no.4
• /
• pp.195-201
• /
• 1998

We have studied the rheological and electrical properties of two types of electrorheological (ER) fluids based on semi-conductive polymers (poly(p-phenylene) and polyaniline). These semi-conductive polymer-based suspensions showed a dramatic increase in viscosity on the application of the static electric field due to the large value of conductivity ratio between particle and medium. The dynamic yield stresses of these ER suspensions exhibited a quadratic dependence on electric field strength at low electric fields and a linear one for high fields. They showed a maximum and then decreased with increasing bulk conductivity of particles. These yield stress behaviors under the static electric field were found to be closely related to the dielectric properties, which is in accord with Maxwell-Wagner interfacial polarization induced by the conductivity effects. In order to achieve better understanding of interfacial polarization effect on ER response and to improve the stability of ER suspension, different kinds of surfactants were employed for controlling the ER activity as well as for enhancing the colloidal stability of suspensions.