• The Journal of the Acoustical Society of Korea
• /
• v.21 no.2
• /
• pp.134-141
• /
• 2002

In this paper, a free wake analysis based on the curved vortex element and CVC wake model is used to predict the aerodynamic performance and noise for HAWT. Also for prediction of RPM, a maximum value through a quadratic regression was suggested. And for a noise prediction, the broadband noise prediction method based on experimental equation was used. The curved vortex element uses a BCVE and an SIVE instead of a straight vertex element. In the CVC wake model, the vortex strengths are assumed to be constant along a span and a vortex filament. The free wake structure made by the curved vortex element and CVC was substituted for a vortex lattice, so it has an advantage for the less calculation time and a depiction of accurate wake structure. For the verification of this program, calculated results are compared with Mr. Kim's experiment model and Zond Z-40FS for performance and with WTS-4 and USWP models for noise. Good agreements are obtained between the predicted and the measured data for the performance and far-field noise spectra.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2020.06a
• /
• pp.86-86
• /
• 2020

수리구조물에 관한 기존 연구들은 대부분 기능성과 안정성 측면에서 본체에 작용하는 유체력에 대한 안정성에 주안점을 두고 있다. 수리구조물 상·하류의 수위차에 기인한 기초지반내의 흐름 및 간극수압 변화는 하천 구조물의 안정성을 연구하는데 매우 중요하다. 해양에서는 파랑하중에 의한 과잉간극수압이 액상화를 발생시켜 해안구조물의 안정에 큰 영향을 미치는 것으로 보고되며, 이에 관련 연구들이 활발하게 진행되고 있다. 반면, 하천구조물 주변 지반의 흐름 및 간극수압 뿐 아니라, 액상화에 관한 연구는 아직 미진한 실정이다. 본 연구에서는 수리구조물 주변의 유동 및 와동 현상 뿐 아니라, 수위차에 따른 지반 내부 유동장과 간극수압에 관한 특성을 분석하기 위해 유체-구조물-지반 비선형 상호작용을 고려할 수 있는 수치수조를 새롭게 제안하였다. 그리고 제안하는 수치수조의 타당성 및 유효성을 검증하기 위해 기존 실험값과 비교·검토를 수행하였고, 그 결과는 거의 유사한 경향을 나타내었다. 또한 이 수치수조에 다양한 입사조건(상·하류 수위차)에 적용하여 유체-구조물-지반의 비선형동적상호간섭 해석을 수행하였다. 최종적으로 수치수조에서 측정한 구조물 주변의 유동, 와동, 수위로부터 수리특성을 논의하였다. 게다가 지반내의 흐름과 간극수압을 측정하여 상·하류 수위차가 수리구조물의 안정성에 미치는 영향을 분석할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.2
• /
• pp.259-266
• /
• 2009

An experimental study was conducted to investigate the effects of forcing amplitude on the flow structure near the nozzle exit of forced jet diffusion flames. The jet was excited up to the blowout occurrence by a considerable large amplitude with a periodic velocity fluctuation at the tube resonating frequency. In the attached flame regime, we disclosed the very interesting result newly that adding of a moderate forcing amplitude caused the jet flame to become longer in spite of being forced. Particular attention is focused on the turnabout mechanism of vortex roll-up around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. From the velocity and flow visualization results, it was ascertained that the surrounding air due to the occurrence of negative velocity parts was suck into the fuel nozzle. To aid in understanding the rotating phenomenon of coherent structure, we present a schematic diagram of the turnabout mechanism of vortex roll-up. The mechanism of vortex turnabout phenomenon can be easily understood by considering the positive and negative velocity amplitudes about the instantaneous velocity of the forcing flow, as shown in this diagram.

• Journal of the KSME
• /
• v.34 no.9
• /
• pp.698-704
• /
• 1994

이 글에서는 난류유동의 수치모사 기법으로서 최근 주목을 받고 있는 LES에 대해서 살펴보았다. LES의 개념은 공간에서의 여고에 근거를 두고 있으며 따라서 난류모델은 작은 스케일의 유동 구조에만 국한된다. LES의 이러한 장점은 DNS에 좀도 가까운 난류모델링의 가능성을 의미한다. 또한 그간 발전된 LES의 기법들에 대해 고찰해보았으며 LES는 DNS의 처선책으로서 난류유 동을 예측하기 위한 도구로서 그 전망은 매우 밝다.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.34 no.4
• /
• pp.297-305
• /
• 2018

Purpose: This study aimed to analyze stress distribution and maximum von Mises stress generated in intracoronal restorations and in tooth structures of mandibular molars with various types of cavity designs and materials. Materials and Methods: Three-dimensional solid models of mandible molar such as O inlay cavity with composite and gold (OR-C, OG-C), MO inlay cavity with composite and gold (MR-C, MG-C), and minimal invasive cavity on occlusal and proximal surfaces (OR-M, MR-M) were designed. To simulate masticatory force, static axial load with total force of 200 N was applied on the tooth at 10 occlusal contact points. A finite element analysis was performed to predict stress distribution generated by occlusal loading. Results: Restorations with minimal cavity design generated significantly lower values of von Mises stress (OR-M model: 26.8 MPa; MR-M model: 72.7 MPa) compared to those with conventional cavity design (341.9 MPa to 397.2 MPa). In tooth structure, magnitudes of maximum von Mises stresses were similar among models with conventional design (372.8 - 412.9 MPa) and models with minimal cavity design (361.1 - 384.4 MPa). Conclusion: Minimal invasive models generated smaller maximum von Mises stresses within restorations. Within the enamel, similar maximum von Mises stresses were observed for models with minimal cavity design and those with conventional design.

• Proceedings of KOSOMES biannual meeting
• /
• 2004.11a
• /
• pp.117-122
• /
• 2004

In order to investigate the initial stage of deep water formation between Vladivostok and the subpolar front in the East Sea, the factors, temperature, salinity, dissolved oxygen, measured by multi-ship surveys in 1969 have been used Deep water formation in the East Sea occurs in essentially two different forms: near continent and open ocean formation the position of eddy derived from potential vorticity matches well with that of deep water formation. The vertical and horizontal distributions of potential vorticity, geostrophic current, temperature, salinity and dissolved oxygen give clues for the preconditioning phase of open ocean formation like a doming of isotherm, associated with a cyclonic circulation

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.7
• /
• pp.79-88
• /
• 2006

In the present paper, the swirl flow structure and flame characteristics of turbulent premixed combustion in a model gas turbine combustor are investigated using large eddy simulation(LES). A G-equation flamelet model is employed to simulate the unsteady flame behavior. When inlet swirl number is increased, the distinct flow structures, such as the shapes of corner recirculation and center toroidal recirculation zone, are observed and the flame length is shorted gradually. Also, the phenomena of flashback are identified at strong swirl intensity. In order to get the accurate description of unsteady flame behavior, the predictive ability of the acoustic wave in a combustor is primarily evaluated. It is found that the vortex generated near the edge of step plays an important role in the flame fluctuation. Finally it is examined systematically that the flame and heat release fluctuation are coupled strongly to the vortex shedding generated by swirl flow and acoustic wave propagation from the analysis of flame-vortex interaction.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.11 no.1 s.22
• /
• pp.77-82
• /
• 2005

In order to investigate the initial stage of deep water formation between Vladivostok and the subpolar front in the East Sea, the factors, temperature, salinity, dissolved oxygen, measured by multi-ship surveys in ]969 have been used. Deep water formation in the .cast Sea occurs in essentially two different forms: near continent and open ocean formation. The position of eddy derived from potential vorticity matches well with that of deep water formation. The vertical and horizontal distributions of potential vorticity, geostrophic current, temperature, salinity and dissolved oxygen give clues for the preconditioning phase qf open ocean formation like a doming of isotherm, associated with a cyclonic circulation.

• Journal of Oral Medicine and Pain
• /
• v.30 no.1
• /
• pp.131-140
• /
• 2005

The purpose of this study was to examine the ablation rate of Er: YAG laser irradiation on dentin and enamel and to observe the microscopic structures of cavities formed after ablation of enamel and dentin in using a bur and cavities formed after ablation using laser. Er:YAG laser irradiated at 200 mJ, 250mJ, 300mJ at the frequency of 20Hz, 15Hz. The following results were obtained : 1. The ablation rate of dentin groups at power of 3 W-6 W was about $1.103{\sim}2.639mm^3/sec$ and there were no significant differences between power of 4.5 W$\sim$6 W. 2. The ablation rate of enamel groups at power of 3 W-6 W was about $0.413{\sim}0.969mm^3/sec$ and there were no significant differences between power of 4 W$\sim$6 W. 3. With SEM examination of the cavity surface treated with the conventional high speed bur revealed relatively flat appearance almost covered with a debris like smear layer. 4. With SEM examination of the lased surface of dentin groups revealed no smear layer and no debris and openings of dentinal tubules were clearly opened. But the lased surfaces of the groups over 3 W were irregular and particles were loosely attached on it. 5. With SEM examination of the lased surface of enamel groups revealed severely destructed surface at the 6 W group and melting drop materials at the 3 W group. But the lased surface of 4 W group revealed clearly ablated surface. Therefore when cutting teeth using Er:YAG laser, the lasing power which can make effective ablation rate and minimize the thermal effect could be 3W at dentin and 4W at enamel. But, further studies and additional data collection will be necessary for appropriate lasing condition of Er:YAG laser.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.8
• /
• pp.1105-1113
• /
• 2003

In the gas wiping process of continuous hot-dip galvanizing, edge overcoating develops near the edge of the steel strip. The overcoating is supposed to occur due to the reduced impact pressure of wiping gas on the strip surface. The purpose of this study is to investigate the effect of edge vortex on the reduced impact pressure. Three-dimensional unsteady flows are simulated using a commercial code, STAR-CD. Standard k-$\varepsilon$ model is used as a turbulence model. It is found that an alternating vortex structure in the vicinity of strip edge is developed by buckling of opposed jet streams and that the reduced amount of impact pressure at strip edge becomes smaller as the air knife gets closer to the strip. The effect of edge baffle on the reduced impact pressure is also investigated.