• 설비공학논문집
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• 제12권8호
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• pp.771-781
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• 2000

The Karman boundary-layer, has been numerically investigated for the disturbance wave number, wave velocity, azimuth angle and radius (Reynolds number, Re). The disturbed flow over rotating disk can lead to transition at a much lower Re than that of the well-known Type 1 mode of instability. This early transition is due to the excitation of the Type II mode. Presented are the neutral stability results concerning these modes by solving new formulated vorticity equations with consideration of whole convective terms. When the present numerical results are compared with the previously known results, the value of critical Re corresponding to Type I is moved from Rec,! =285.3 to 270.2 and the value corresponding to Type II is from $Re_{c,2}$=69.4 to 36.9, respectively. Also, the corresponding wave number is moved from $k_1$ =0.378 to $k_1$ =0.389 for Type I; from $k_2$ =0.279 to $k_2$=0.385 for Type II. For Type II, the upper limit of wave number and azimuth angle is $k_U$=0.5872,$varepsilon_U=-18^{\circ}$ , while its lower limit is$k_L$ =0.05, $varepsilon_L=-27^{\circ}$ This implies that the disturbances will be relatively fast amplified at small Re and within narrow bands of wave number compared with the previous results.

• 반도체디스플레이기술학회지
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• 제9권4호
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• pp.13-18
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• 2010

Extreme ultraviolet (EUV) lithography using 13.5 nm wavelengths is expected to be adopted as a mass production technology for 32 nm half pitch and below. One of the new issues introduced by EUV lithography is the shadowing effect. Mask shadowing is a unique phenomenon caused by using mirror-based mask with an oblique incident angle of light. This results in a horizontal-vertical (H-V) biasing effect and ellipticity in the contact hole pattern. To minimize the shadowing effect, a refilled mask is an available option. The concept of refilled mask structure can be implemented by partial etching into the multilayer and then refilling the trench with an absorber material. The simulations were carried out to confirm the possibility of application of refilled mask in 32 nm line-and-space pattern under the condition of preproduction tool. The effect of sidewall angle in refilled mask is evaluated on image contrast and critical dimension (CD) on the wafer. We also simulated the effect of refilled absorber thickness on aerial image, H-V CD bias, and overlapping process window. Finally, we concluded that the refilled absorber thickness for minimizing shadowing effect should be thinner than etched depth.

• 산업경영시스템학회지
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• 제31권4호
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• pp.146-152
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• 2008

This study was aimed to understand the effects of perturbed floor surface on human postural stability while standing. Ten subjects were asked to stand quietly on the surface with two angles of inclination ($0^{\circ}$ and $5^{\circ}$), two contamination conditions (dry and oil-contaminated), and three commercial floor materials (ceramic tile, coated wood, and vinyl tile). During each trial, a force plate with data acquisition systems was used to collect subject's center of pressure (COP) position. Measured COPs were then converted into the length of postural sway path in both subject's anterior-posterior (AP) and medio-lateral (ML) axis. Results showed that the length of sway path in ML axis was significantly affected by the angle of inclination and the type of floor material. The sway length was increased significantly at the inclination angle of $5^{\circ}$ and on the vinyl tile, respectively. The contamination condition, however, did not significantly affect the postural sway length in both AP and ML axis. The results imply that a proper treatment of floor surface and material is critical to preserving postural balance while standing.

• 대한기계학회논문집
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• 제12권6호
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• pp.1407-1414
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• 1988

본 연구에서는 저자들에 의해 이미 개발된 경계유선수정법에 의한 B-B 유동계 산을 통해 익열의 편차각을 계산하고 기존의 예측방법에 의한 결과와 비교 검토하여 압축성 및 3차원 비축대칭성의 효과를 검토하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.333-339
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• 2003

Steady and unsteady cavitation characteristics of turbopump inducer were investigated in this paper. To see the effect of blade angle on the inducer performance, three inducers with inlet tip blade angle of $7.8^{\circ},\;7.0^{\circ},\;6.1^{\circ}$, respectively, were tested. For $7.8^{\circ},\;7.0^{\circ}$ inducers in the non-cavitating condition, head decreased linearly with flow rate, but head-flow rate curve had a dip at the flow coefficient ${\Phi}=0.065\;for\;6.1^{\circ}$ inducer. Rotating cavitation and cavitation surge were found in the $7.8^{\circ},\;7.0^{\circ}$ inducers in the cavitation tests. During the rotating cavitation one cell rotated at the same rotational speed as that of the inducer. The cavitation surge did not rotate and the oscillating frequency was $7{\sim}20\;Hz$. From the curve of the critical cavitation number versus flow rate, it was found that the steady cavitation performance of $6.1^{\circ}$ inducer was much lower than that of $7.8^{\circ},\;7.0^{\circ}$ inducers.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2180-2186
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• 2002

In a micro-scale contact, capillary force and van der Waals interaction significantly influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (wet angle), relative humidity and deformation of asperities in the real area of contact. A better understanding of these surface forces is of great necessity in order to find a solution for reducing friction and adhesion of micro surfaces. The objective of this study is to investigate the surface forces in micro-scale rough surface contact. We proposed an effective method to analyze capillary and van der Waals forces in micro-scale contact. In this method, Winkler spring model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height images. Self-mated contact of DLC(diamond like carbon) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidity and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• Geomechanics and Engineering
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• 제18권1호
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• pp.21-27
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• 2019

Rockburst disasters pose serious threat to mining safety and underground excavation, especially in China, resulting in massive life-wealth loss and even compulsive closed-down of some coal mines. To investigate the mechanism of rockbursts that occur under a state of static forces, a stress model with sidewall as prototype was developed and verified by a group of laboratory experiments and numerical simulations. In this model, roadway sidewall was simplified as a square plate with axial compression and end (horizontal) restraints. The stress field was solved via the Airy stress function. To track the "closeness degree" of the stress state approaching the yield limit, an unbalanced force F was defined based on the Mohr-Coulomb yield criterion. The distribution of the unbalanced force in the plane model indicated that only the friction angle above a critical value could cause the first failure on the coal in the deeper of the sidewall, inducing the occurrence of rockbursts. The laboratory tests reproduced the rockburst process, which was similar to the prediction from the theoretical model, numerical simulation and some disaster scenes.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.769-780
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• 2022

This paper studies the dynamic behavior of laminated composite circular cylindrical shells interacting with a fluid. The mathematical formulation of the dynamic problem for an elastic body is developed based on the variational principle of virtual displacements and the relations of linear elasticity theory. The behavior of an ideal compressible fluid is described by the potential theory, the equations of which together with boundary conditions are transformed to a weak form. The hydrodynamic pressure exerted by the fluid on the internal surface of the shell is calculated according to the linearized Bernoulli equation. The numerical implementation of the mathematical formulation has been done using the semi-analytical finite element method. The influence of the ply angle and lay-up configurations of laminated composites on the natural vibration frequencies and the hydroelastic stability boundary have been analyzed for shells with different geometrical dimensions and under different kinematic boundary conditions set at their edges. It has been found that the optimal value of the ply angle depends on the level of filling of the shell with a fluid. The obtained results support the view that by choosing the optimal configuration of the layered composite material it is possible to change upwards or downwards the frequency and mode shape, as well as the critical velocity for stability loss over a wide range.

• Current Optics and Photonics
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• 제6권1호
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• pp.79-85
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• 2022

Tracers are one of the critical factors for improving the performance of velocimetry. Silver and gold nanoparticles as tracers with localized surface-plasmon resonance are analyzed for their scattering properties. The scattering cross sections, angular distribution of the scattering, and equivalent scattering cross sections from 53° and 1.5° half-angle cones at 532 nm are calculated, with particle sizes in the nanoscale range. The 53° and 1.5° half-angle cones used as examples correspond respectively to the collection cones for microscope objectives in microscopic measurements and camera lenses in macroscopic measurements. We find that there is a transitional size near 35 nm when comparing the equivalent scattering cross sections between silver and gold nanoparticles in water at 532 nm. The equivalent scattering cross section of silver nanoparticles is greater or smaller than that of gold nanoparticles when the particle radius is greater or smaller than 35 nm respectively. When the radius of the plasmonic nanoparticles is smaller than about 44 nm, their equivalent scattering cross sections are at least ten times that of TiO₂ nanoparticles. Plasmonic nanoparticles are promising for velocimetry applications.

• 한국음향학회지
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• 제25권1호
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• pp.1-6
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• 2006

천해에서의 수중음장 계산에서 음향 임피던스를 해저면 입력인자로서 도입하는 방안의 가능성을 고찰하였다. 먼저 탄성 해저면에서의 음파반사 특성을 고찰한 결과, 임계 접지각 이하에서 음향 임피던스는 접지각이 거의 $0^{\circ}$에 가까울 때의 임피던스 $Z_0$ 1개 값으로 근사가 가능함을 나타내었다. 이러한 특성과 'effective depth' 개념을 접목시켜 전달손실을 계산한 결과, 수중음장 계산에서 임피던스를 해저면 음향 특성을 나타내는 입력인자로 사용하는 것이 가능성이 있음을 확인하였다.