• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.469-475
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• 2003

The performance of a centrifugal compressor composed of an impeller, tandem diffuser rows and axial guide vanes has been predicted numerically and compared with available experimental results on its design rotational speed. The pitchwise-averaged mixing plane method was employed for the boundaries between rotor and stator to obtain steady state solutions. The overall characteristics showed differently according to the relative positions of tandem diffuser rows while the characteristics of impeller showed almost identical. The numerical results agree with the measured data in respect of their tendency. It turned out that 0% of relative positions is the worst case in terms of static pressure recovery and efficiency. According to the experimental results, some pressure fluctuations and malfunction of the compressor were observed for 75% case. However, this numerical calculation using mixing plane method did not capture any of those phenomena. Thus, unsteady flow calculation should be performed to investigate the stability of the compressor caused by different diffuser configuration.

• Steel and Composite Structures
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• 제28권4호
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• pp.427-438
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• 2018

Static stability is a decisive factor in the design of domes. Stability-related external factors, such as load and supports, are incorporated into structural vulnerability theory by the definition of a relative rate of joint well-formedness ($r_r$). Hence, the instability mechanism of domes can be revealed. To improve stability, an optimization model against instability, which takes the maximization of the lowest $r_r$ ($r_{r,min}$) as the objective and the discrete member sections as the variables, is established with constraints on the design requirements and steel consumption. Optimizations are performed on two real-life Kiewitt-6 model domes with a span of 23.4 m and rise of 11.7 m, which are initially constructed for shaking table collapse test. Well-formedness analyses and stability calculation (via arc-length method) of the models throughout the optimization history demonstrate that this proposed method can effectively enhance $r_{r,min}$ and optimize the static stability of shell-like structures. Additionally, seismic performance of the optimum models subjected to the same earthquake as in the shaking table test is checked. The supplemental simulations prove that the optimum models are superior to the original models under earthquake load as well.

• Journal of the Korean Wood Science and Technology
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• 제20권3호
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• pp.29-37
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• 1992

This research was carried out to investigate the effects of cyclic humidification on the dimensional stability of particleboard manufactured according the three specific gravity levels and com-ply fabricated with a core of particleboard and veneer or plywood as the face and back materials. Both the particleboard and com-ply were subjected to four cycles of 50-90-50% relative humidity. The results are summarized as follows: Particleboard and com-ply followed a clear pattern of increasing dimensions and weight on the adsorption cycle and decreasing dimensions and weight on the humidification cycle. After the fourth cycle, the dimensions and weight of both particleboard and com-ply were greater than those originally measured. The greater part of increase in occurred during the first humidification cycle. The specific gravity of particleboard has a significant effect thickness and volume change. The dimensional stability of com-ply was better than that of particleboard. In addition, the dimensional stability of com-ply bonded with plywood was better than that of com-ply bonded with veneer.

• 펄프종이기술
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• 제43권4호
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• pp.31-39
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• 2011

One of the main drawbacks of wood fibers based composite materials are their tendency to swell due to moisture uptake in wet and moist environments. The main contribution to the hygroexpansion usually comes from the hydrophilic wood fibers. Recent trend toward the high speed printing, copying, and precision converting precesses demands a high level of dimensional stability under various environmental conditions. The purpose of this study was to investigate the dimensional stability of softwood bleached kraft pulp handsheets depending on wet pressing conditions. By increasing the number of wet pressing, dimensional stability was decreased because of increased fiber-to-fiber bonding. Hygroexpansion of handsheets had a linear relationship with the relative bonded area and equilibrium moisture contents. Dip elongation was decreased when the number of wet pressing was increased because of increased fiber-to-fiber bonding to resist low load in water.

• 통합자연과학논문집
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• 제3권2호
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• pp.89-95
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• 2010

It is still controversial where the improved stability of n-octadecyltriethoxysilane self-assembled monolayer (OTE SAM) on plasma-pretreated mica surface exactly originates from. To date, it has been well known that the extensive cross-polymerization between silane head-groups is a crucial factor for the outstanding mechanical strength of the monolayer. However, this study clearly showed that the stability comes not only from the cross-links but also, far more importantly, from the direct chemical bonds between silane headgroups and mica surface. To examine this phenomenon, n-octadecyltrichlorosilane monolayers were self-assembled on both untreated and plasma treated mica surfaces, and their adhesion properties at various physical conditions (relative humidity, high stress, and contact repetition) were investigated and compared through the use of the surface forces apparatus technique. It revealed that, in highly humid conditions (>90%RH), there is a substantial difference of stability between untreated and plasma treated cases and the plasma treated surface is mechanically much more stable. It obviously proves that the extensive chemical bonds indeed exist between silane head-groups and plasma treated mica surface and dramatically improve the mechanical stability of the OTE monolayer-coated mica substrate.

• 한국자기학회지
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• 제5권5호
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• pp.543-547
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• 1995

A set of $Fe_{1-x}Ni_{x}$ (x=0.10, 0.25, 0.30, 0.35, 0.50, 0.60, 0.75, 0.85) fine particles prepared by the gas evaporation technique was studied by $M\"{o}ssbauer$, XRD and other techniques. The XRD and $M\"{o}ssbauer$ patterns of the sample with x=0.10 ($Fe_{90}Ni_{10}$) were found to be exceptionally different, showing an austenite phase stability when the particles are quenched. This phase stability is quite different from that of the corresponding bulk alloy. Using binomial distrbution fits of the $M\"{o}ssbauer$ spectra of the particles in terms of nearest and next nearest neighbour configurations around the Fe atoms, an analysis of this phase stability is given. The changes in the relative intensities of the resulting magnetic sextets are used to determine the increase in martensite following the austenite-martensite transformation process. The stable austenite can, therefore, be determined. This stability may be related to the oxide surface layer and the small number of atoms of these fine particles.

• 한국자원식물학회지
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• 제21권6호
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• pp.435-439
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• 2008

Due to the fact that tocopherols and tocotrienols have antioxidant and anticancer properties, the commercial utilization of unsaponifiable fractions in rice bran is increasing. These nutraceutical compounds, however, are fairly unstable and readily break down when exposed to oxygen or lighting conditions. To compare the relative sensitivity of vit E isomers to heat and oxygen, concentrated unsaponifiable fractions extracted from crude rice bran oil were exposed to various temperature, oxygen (nitrogen-balanced), and bathing solvent conditions and resultant concentration changes in ${\alpha}$- and ${\gamma}$-tocopherols (T) and tocotrienols (T3) were evaluated. Each isomer exhibited different heat stability. Among them, ${\alpha}$-T3 degraded more rapidly compared to other vit E isomers while ${\alpha}$-T was the most stable isomer. Oxygen level also showed significant impact on each isomer's stability where severe reductions of ${\gamma}$-T (by 20%) and ${\gamma}$-T3 (by 29%) were observed under 2% oxygen conditions, while under 0% oxygen conditions no degradation could be observed even after exposure to $95^{\circ}C$ for 4 hours. When various blending solvents were mixed with concentrated unsaponifiable fractions, organic solvents such as isooctane and hexane were more effective in maintaining the stability of ${\gamma}$- T3 compared to edible oils, among which com oil was more efficient than soybean and rice bran oils.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.156-161
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• 1999

new bearing concept, the wave journal bearing, has been developed to improve the static and dynamic performances of an air-lubricated hydrodynamic journal bearing. This concept features waves on bearing surface. In this study, we present the solution of the compressible Reynolds equation valid for arbitrary Knudsen numbers. Straight wave journal bearing is investigated numerically. The performances of straight wave bearing are compared to the plain journal bearing over relatively wide range of bearing number and eccentricity. The wave journal bearing offers better stability than the plain journal bearing under a13 bearing numbers covered in this study. The bearing load and stability characteristics are dependent on the geometric parameters such as the amplitude and the starting point of the wave relative to the applied load. Under the condition of Knudsen number)0.01, we can not ignore the effect of slip for journal bearing.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제31회 춘계학술대회
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• pp.153-158
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• 2000

The purpose of present paper is to prove an improvement on stability of plane Journal bearing due to the leaf spring damper(LSD) experimentally A flexible rotor system is designed and manufackuea in order to generate oil whip instability of journal bearing at relative lower rotating speed. Vibration amplitude and instability onset speeds are investigated for a conventional plane journal bearing and plane journal bearing with LSD. To investigate the damping effects of LSD on stability of bearing, experiments are also conducted on the leaf spring dampers with and without working oil. It is found that the leaf spring damper can considerably increase the instability onset speed of a plane journal bearing.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.180-185
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• 2003

In order to enhance dexterity in execution of robot tasks, a redundant number of degrees-of-freedom (DOF) is adopted for design of robotic mechanisms like robot arms and multi-fingered robot hands. Associated with such redundancy in the number of DOFs relative to the number of physical variables necessary and sufficient for description of a given task, an extra performance index is introduced for controlling such a redundant robot in order to avoid arising of an ill-posed problem of inverse kinematics from the task space to the joint space. This paper shows that such an ill-posedness of DOF redundancy can be resolved in a natural way by using a novel concept named “stability on a manifold”. To show this, two illustrative robot tasks 1) robotic handwriting and 2) control of an object posture via rolling contact by a multi-DOF finger are analyzed in details.