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1.
The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now. In most cases of experimental approaches, the accurate and objective decision of cavitation inception is primary, which is the main topic of this paper. Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise, a faithful exploration cannot be made especially for the cavitation inception. Alternatively, the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception. This study, hence, employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis, both which are appropriate for finding such a repeating frequency. Through the acoustical measurement in a water tunnel, the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation. 相似文献
2.
LEE Jeung-Hoon JUNG Jae-Kwon LEE Kyung-Jun HAN Jae-Moon PARK Hyung-Gil SEO Jong-Soo 《水动力学研究与进展(B辑)》2012,24(5):658-667
Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy. 相似文献
3.
Jong-Soo Kim Yong-Bim Im Ngoc-Hung Bui 《Journal of Mechanical Science and Technology》2005,19(9):1790-1800
The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid
in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion
is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper,
a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs
and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant
effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs
and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the
frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference
between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation
frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency
of oscillation. Also the average temperature of vapor plugs decreased. 相似文献
4.
In Part 1 of this study, an advanced numerical simulation method was proposed to investigate the impact characteristics of the KN-18 spent nuclear fuel (SNF) transport cask recently developed in Korea and verified against the experimental results. 相似文献
5.
Jong-Soo Bae Joo-Won Park Jae-Ho Kim Jae-Goo Lee Younghun Kim Choon Han 《Korean Journal of Chemical Engineering》2010,27(5):1458-1461
The concept of “waste-to-wealth” is spreading awareness to prevent global warming and recycle the restrictive resources. To
contribute towards sustainable development, hydrogen energy is obtained from syngas (CO and H2) generated from waste gasification, followed by CO oxidation and CO2 removal. In H2 generation, it is key to produce more purified H2 from syngas using heterogeneous catalysts. In this respect, we prepared Pt/Al2O3 catalyst with nanoporous structure using precipitation method, and compared its catalytic activity with commercial alumina
(Degussa). Based on the results of XRD and TEM, it was found that metal particles did not aggregate on the alumina surface
and showed high dispersion. Optimum condition for CO conversion was 1.5 wt% Pt loaded on Al2O3 support, and pure hydrogen was obtained after removal of CO2 gas. 相似文献
6.
Sang-Hee Yoon Jong-Soo Oh Young-Ho Lee Seok-Woo Lee 《IEEE transactions on magnetics》2005,41(7):2300-2306
This paper describes miniaturized inertia generators for converting mechanical energy into electrical energy for military applications, especially as power supplies for electrical fuzes. In order to minimize the volume of the generators, our design adopted a ring-shaped magnet enclosing a coil assembly. The inertia generators are intended not to ignite an electrical detonator but to charge a capacitor that drives the electric circuit of fuze. A mechanical safety system, a shear plate, is used as a release mechanism for the inertia generators to prevent them from operating accidentally. We designed the inertia generators by using the simulation results of an electromagnetic analysis tool. In an experimental study, we performed safety tests on the shear plate and firing tests of the fabricated inertia generators. The present inertia generators show that a voltage of 14.2 V was charged on a capacitor of 30 /spl mu/F within the charging time of 0.68 ms and the critical acceleration for safety was 5000 G, verifying that the inertia generators can be used as power supplies for small-caliber electrical fuzes. 相似文献
7.
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9.
Jong-Soo Choi 《Journal of Mechanical Science and Technology》1994,8(2):161-174
The objective of this research was to identify which aspects of the fluid dynamics are associated with noise generation in centrifugal turbomachinery. Research emphasis was placed on the generation of noise at frequencies other than the blade passage tones. In order to avoid noise generated by the interaction of the discharged flow and stationary objects outside of the impeller, experiments are performed on a centrifugal impeller without diffuser and casing. With this discharge configuration, the radiated noise spectra are shown to be dominated by harmonically related broad humps at low frequency. These were proven to be generated by the interaction of a coherent unsteady flow structure rotating around the impeller discharge and the trailing edges of the impeller blades. 相似文献
10.
Jongsoo Jurng Nahmkeon Hur Kwang Ho Kim Chun Sik Lee 《Journal of Mechanical Science and Technology》1993,7(4):312-319
A numerical simulation is carried out to analyze the flow field of cooling air through the radiator and engine compartment. In order to consider the strong effect of the suction-type flow by the cooling fan at engine idling condition, a potential flow analysis is attempted by the assumption of a line sink located at the position of the cooling fan. The governing equations for steady two-dimensional, incompressible, turbulent flow are solved with the two-equationk-ε model for turbulence. The velocity profiles in the underhood engine compartment and around the front-end of a real vehicle are measured to compare with the numerical results. The agreement between the numerical and experimental results is fairly good. It is concluded that a two-dimensional computation is a fast and efficient tool for predicting the effect of front-end design on the cooling air flow through the radiator. 相似文献